diff --git a/Libraries/SPTarkov.Server.Core/Controllers/DialogueController.cs b/Libraries/SPTarkov.Server.Core/Controllers/DialogueController.cs
index 2a4f8833..08e696d7 100644
--- a/Libraries/SPTarkov.Server.Core/Controllers/DialogueController.cs
+++ b/Libraries/SPTarkov.Server.Core/Controllers/DialogueController.cs
@@ -638,10 +638,7 @@ public class DialogueController(
 
         // Only add the profile to the friends list if it doesn't already exist
         var profile = saveServer.GetProfile(sessionID);
-        if (!profile.FriendProfileIds.Contains(request.To.Value))
-        {
-            profile.FriendProfileIds.Add(request.To.Value);
-        }
+        profile.FriendProfileIds.Add(request.To.Value);
 
         // We need to delay this so that the friend request gets properly added to the clientside list before we accept it
         _ = new Timer(
@@ -677,11 +674,7 @@ public class DialogueController(
     public virtual void DeleteFriend(MongoId sessionID, DeleteFriendRequest request)
     {
         var profile = saveServer.GetProfile(sessionID);
-        var friendIndex = profile.FriendProfileIds.IndexOf(request.FriendId);
-        if (friendIndex != -1)
-        {
-            profile.FriendProfileIds.RemoveAt(friendIndex);
-        }
+        profile?.FriendProfileIds?.Remove(request.FriendId);
     }
 
     /// <summary>
diff --git a/Libraries/SPTarkov.Server.Core/Controllers/QuestController.cs b/Libraries/SPTarkov.Server.Core/Controllers/QuestController.cs
index 58273c80..06c24d3a 100644
--- a/Libraries/SPTarkov.Server.Core/Controllers/QuestController.cs
+++ b/Libraries/SPTarkov.Server.Core/Controllers/QuestController.cs
@@ -226,7 +226,7 @@ public class QuestController(
             }
 
             handedInCount = int.Parse(condition.Value.ToString());
-            isItemHandoverQuest = condition.ConditionType == handoverQuestTypes.FirstOrDefault();
+            isItemHandoverQuest = condition.ConditionType == handoverQuestTypes.FirstOrDefault(); // TODO: there's 2 values, why does it only check for the first
             handoverRequirements = condition;
 
             if (pmcData.TaskConditionCounters.TryGetValue("ConditionId", out var counter))
@@ -312,7 +312,9 @@ public class QuestController(
             else
             {
                 // Remove item with children
-                var toRemove = pmcData.Inventory.Items.GetItemWithChildrenTpls(itemHandover.Id);
+                var toRemove = pmcData
+                    .Inventory.Items.GetItemWithChildrenTpls(itemHandover.Id)
+                    .ToHashSet();
                 var index = pmcData.Inventory.Items.Count;
 
                 // Important: don't tell the client to remove the attachments, it will handle it
diff --git a/Libraries/SPTarkov.Server.Core/Extensions/ItemExtensions.cs b/Libraries/SPTarkov.Server.Core/Extensions/ItemExtensions.cs
index ec03e463..83e32c4e 100644
--- a/Libraries/SPTarkov.Server.Core/Extensions/ItemExtensions.cs
+++ b/Libraries/SPTarkov.Server.Core/Extensions/ItemExtensions.cs
@@ -365,7 +365,7 @@ namespace SPTarkov.Server.Core.Extensions
         /// </summary>
         /// <param name="items">Inventory items to look for secure container in</param>
         /// <returns>List of ids</returns>
-        public static List<MongoId> GetSecureContainerItems(this IEnumerable<Item> items)
+        public static HashSet<MongoId> GetSecureContainerItems(this IEnumerable<Item> items)
         {
             var secureContainer = items.First(x => x.SlotId == "SecuredContainer");
 
@@ -378,7 +378,7 @@ namespace SPTarkov.Server.Core.Extensions
             var itemsInSecureContainer = items.GetItemWithChildrenTpls(secureContainer.Id);
 
             // Return all items returned and exclude the secure container item itself
-            return itemsInSecureContainer.Where(x => x != secureContainer.Id).ToList();
+            return itemsInSecureContainer.Where(x => x != secureContainer.Id).ToHashSet();
         }
 
         /// <summary>
diff --git a/Libraries/SPTarkov.Server.Core/Extensions/ProfileExtensions.cs b/Libraries/SPTarkov.Server.Core/Extensions/ProfileExtensions.cs
index 80e5f40f..90200f6b 100644
--- a/Libraries/SPTarkov.Server.Core/Extensions/ProfileExtensions.cs
+++ b/Libraries/SPTarkov.Server.Core/Extensions/ProfileExtensions.cs
@@ -209,7 +209,7 @@ namespace SPTarkov.Server.Core.Extensions
         /// <param name="item">Item to check</param>
         /// <param name="rootId">Root item id to check for</param>
         /// <returns>True when item has rootId, false when not</returns>
-        public static bool DoesItemHaveRootId(this PmcData pmcData, Item item, string rootId)
+        public static bool DoesItemHaveRootId(this PmcData pmcData, Item item, MongoId rootId)
         {
             var currentItem = item;
             while (currentItem is not null)
@@ -235,7 +235,7 @@ namespace SPTarkov.Server.Core.Extensions
         /// <param name="pmcData">Profile to search</param>
         /// <param name="questId">Quest id to look up</param>
         /// <returns>QuestStatus enum</returns>
-        public static QuestStatusEnum GetQuestStatus(this PmcData pmcData, string questId)
+        public static QuestStatusEnum GetQuestStatus(this PmcData pmcData, MongoId questId)
         {
             var quest = pmcData.Quests?.FirstOrDefault(q => q.QId == questId);
 
diff --git a/Libraries/SPTarkov.Server.Core/Extensions/TraderAssortExtensions.cs b/Libraries/SPTarkov.Server.Core/Extensions/TraderAssortExtensions.cs
index 55a7bf1e..c62ca6fb 100644
--- a/Libraries/SPTarkov.Server.Core/Extensions/TraderAssortExtensions.cs
+++ b/Libraries/SPTarkov.Server.Core/Extensions/TraderAssortExtensions.cs
@@ -34,7 +34,7 @@ namespace SPTarkov.Server.Core.Extensions
             assort.LoyalLevelItems.Remove(itemId);
 
             // The item being removed may have children linked to it, find and remove them too
-            var idsToRemove = assort.Items.GetItemWithChildrenTpls(itemId);
+            var idsToRemove = assort.Items.GetItemWithChildrenTpls(itemId).ToHashSet();
             assort.Items.RemoveAll(item => idsToRemove.Contains(item.Id));
 
             return assort;
@@ -47,7 +47,7 @@ namespace SPTarkov.Server.Core.Extensions
         /// <param name="itemsTplsToRemove">Item TPLs the assort should not have</param>
         public static void RemoveItemsFromAssort(
             this TraderAssort assortToFilter,
-            HashSet<string> itemsTplsToRemove
+            HashSet<MongoId> itemsTplsToRemove
         )
         {
             assortToFilter.Items = assortToFilter
diff --git a/Libraries/SPTarkov.Server.Core/Generators/BotEquipmentModGenerator.cs b/Libraries/SPTarkov.Server.Core/Generators/BotEquipmentModGenerator.cs
index bdb10494..620d6a2f 100644
--- a/Libraries/SPTarkov.Server.Core/Generators/BotEquipmentModGenerator.cs
+++ b/Libraries/SPTarkov.Server.Core/Generators/BotEquipmentModGenerator.cs
@@ -197,7 +197,8 @@ public class BotEquipmentModGenerator(
                 );
                 switch (plateSlotFilteringOutcome.Result)
                 {
-                    case Result.UNKNOWN_FAILURE or Result.NO_DEFAULT_FILTER:
+                    case Result.UNKNOWN_FAILURE
+                    or Result.NO_DEFAULT_FILTER:
                         if (logger.IsLogEnabled(LogLevel.Debug))
                         {
                             logger.Debug(
@@ -1535,7 +1536,10 @@ public class BotEquipmentModGenerator(
         // Filtering mod pool to item that wasn't already there can have problems;
         // You'd have a mod being picked without any sub-mods in its chain, possibly resulting in missing required mods not being added
         // Mod is in existing mod pool
-        if (request.ItemModPool[request.ModSlot].Contains(matchingModFromPreset.Template))
+        if (
+            request.ItemModPool.TryGetValue(request.ModSlot, out var ids)
+            && ids.Contains(matchingModFromPreset.Template)
+        )
         // Found mod on preset + it already exists in mod pool
         {
             return [matchingModFromPreset.Template];
@@ -2056,7 +2060,7 @@ public class BotEquipmentModGenerator(
     public HashSet<MongoId> FilterSightsByWeaponType(
         Item weapon,
         HashSet<MongoId> scopes,
-        Dictionary<MongoId, List<MongoId>> botWeaponSightWhitelist
+        Dictionary<MongoId, HashSet<MongoId>> botWeaponSightWhitelist
     )
     {
         var weaponDetails = itemHelper.GetItem(weapon.Template);
diff --git a/Libraries/SPTarkov.Server.Core/Generators/LocationLootGenerator.cs b/Libraries/SPTarkov.Server.Core/Generators/LocationLootGenerator.cs
index 306cecfc..f11e8fde 100644
--- a/Libraries/SPTarkov.Server.Core/Generators/LocationLootGenerator.cs
+++ b/Libraries/SPTarkov.Server.Core/Generators/LocationLootGenerator.cs
@@ -154,11 +154,9 @@ public class LocationLootGenerator(
         // Remove christmas items from loot data
         if (!_seasonalEventService.ChristmasEventEnabled())
         {
-            allStaticContainersOnMapClone = allStaticContainersOnMapClone
-                .Where(item =>
-                    !_seasonalEventConfig.ChristmasContainerIds.Contains(item.Template.Id)
-                )
-                .ToList();
+            allStaticContainersOnMapClone = allStaticContainersOnMapClone.Where(item =>
+                !_seasonalEventConfig.ChristmasContainerIds.Contains(item.Template.Id)
+            );
         }
 
         var staticRandomisableContainersOnMap = GetRandomisableContainersOnMap(
@@ -561,7 +559,8 @@ public class LocationLootGenerator(
         // Some containers need to have items forced into it (quest keys etc.)
         var tplsForced = staticForced
             .Where(forcedStaticProp => forcedStaticProp.ContainerId == containerClone.Template.Id)
-            .Select(x => x.ItemTpl);
+            .Select(x => x.ItemTpl)
+            .ToHashSet();
 
         // Draw random loot
         // Allow money to spawn more than once in container
@@ -914,9 +913,9 @@ public class LocationLootGenerator(
             // Ensure no seasonal items are in pool if not in-season
             if (!seasonalEventActive)
             {
-                spawnPoint.Template.Items = spawnPoint
-                    .Template.Items.Where(item => !seasonalItemTplBlacklist.Contains(item.Template))
-                    .ToList();
+                spawnPoint.Template.Items = spawnPoint.Template.Items.Where(item =>
+                    !seasonalItemTplBlacklist.Contains(item.Template)
+                );
             }
 
             // Spawn point has no items after filtering, skip
diff --git a/Libraries/SPTarkov.Server.Core/Generators/RepeatableQuestGeneration/CompletionQuestGenerator.cs b/Libraries/SPTarkov.Server.Core/Generators/RepeatableQuestGeneration/CompletionQuestGenerator.cs
index 35ce1510..79309af1 100644
--- a/Libraries/SPTarkov.Server.Core/Generators/RepeatableQuestGeneration/CompletionQuestGenerator.cs
+++ b/Libraries/SPTarkov.Server.Core/Generators/RepeatableQuestGeneration/CompletionQuestGenerator.cs
@@ -119,7 +119,7 @@ public class CompletionQuestGenerator(
             traderId,
             repeatableConfig,
             completionConfig,
-            selectedItems
+            selectedItems.ToHashSet()
         );
 
         return quest;
diff --git a/Libraries/SPTarkov.Server.Core/Generators/RepeatableQuestGeneration/EliminationQuestGenerator.cs b/Libraries/SPTarkov.Server.Core/Generators/RepeatableQuestGeneration/EliminationQuestGenerator.cs
index 66128823..a87b6f75 100644
--- a/Libraries/SPTarkov.Server.Core/Generators/RepeatableQuestGeneration/EliminationQuestGenerator.cs
+++ b/Libraries/SPTarkov.Server.Core/Generators/RepeatableQuestGeneration/EliminationQuestGenerator.cs
@@ -636,7 +636,7 @@ public class EliminationQuestGenerator(
             // Filter out close range weapons from far distance requirement
             case > 50:
             {
-                List<string> weaponTypeBlacklist = ["Shotgun", "Pistol"];
+                HashSet<string> weaponTypeBlacklist = ["Shotgun", "Pistol"];
 
                 // Filter out close range weapons from long distance requirement
                 generationData.WeaponCategoryRequirementConfig.RemoveAll(category =>
@@ -647,7 +647,7 @@ public class EliminationQuestGenerator(
             // Filter out long range weapons from close distance requirement
             case < 20:
             {
-                List<string> weaponTypeBlacklist = ["MarksmanRifle", "DMR"];
+                HashSet<string> weaponTypeBlacklist = ["MarksmanRifle", "DMR"];
 
                 // Filter out far range weapons from close distance requirement
                 generationData.WeaponCategoryRequirementConfig.RemoveAll(category =>
diff --git a/Libraries/SPTarkov.Server.Core/Generators/RepeatableQuestGeneration/RepeatableQuestRewardGenerator.cs b/Libraries/SPTarkov.Server.Core/Generators/RepeatableQuestGeneration/RepeatableQuestRewardGenerator.cs
index 88f916ff..9616c775 100644
--- a/Libraries/SPTarkov.Server.Core/Generators/RepeatableQuestGeneration/RepeatableQuestRewardGenerator.cs
+++ b/Libraries/SPTarkov.Server.Core/Generators/RepeatableQuestGeneration/RepeatableQuestRewardGenerator.cs
@@ -64,7 +64,7 @@ public class RepeatableQuestRewardGenerator(
         MongoId traderId,
         RepeatableQuestConfig repeatableConfig,
         BaseQuestConfig eliminationConfig,
-        List<MongoId>? rewardTplBlacklist = null
+        HashSet<MongoId>? rewardTplBlacklist = null
     )
     {
         // Get vars to configure rewards with
diff --git a/Libraries/SPTarkov.Server.Core/Generators/WeaponGen/Implementations/ExternalInventoryMagGen.cs b/Libraries/SPTarkov.Server.Core/Generators/WeaponGen/Implementations/ExternalInventoryMagGen.cs
index 99368c61..3eedc338 100644
--- a/Libraries/SPTarkov.Server.Core/Generators/WeaponGen/Implementations/ExternalInventoryMagGen.cs
+++ b/Libraries/SPTarkov.Server.Core/Generators/WeaponGen/Implementations/ExternalInventoryMagGen.cs
@@ -40,7 +40,7 @@ public class ExternalInventoryMagGen(
         var magTemplate = inventoryMagGen.GetMagazineTemplate();
         var magazineTpl = magTemplate.Id;
         var weapon = inventoryMagGen.GetWeaponTemplate();
-        List<MongoId> attemptedMagBlacklist = [];
+        HashSet<MongoId> attemptedMagBlacklist = [];
         var defaultMagazineTpl = weapon.GetWeaponsDefaultMagazineTpl();
         var isShotgun = itemHelper.IsOfBaseclass(weapon.Id, BaseClasses.SHOTGUN);
 
@@ -176,7 +176,7 @@ public class ExternalInventoryMagGen(
     /// <returns> Item of chosen magazine </returns>
     public TemplateItem? GetRandomExternalMagazineForInternalMagazineGun(
         MongoId weaponTpl,
-        List<MongoId> magazineBlacklist
+        HashSet<MongoId> magazineBlacklist
     )
     {
         // The mag Slot data for the weapon
diff --git a/Libraries/SPTarkov.Server.Core/Helpers/AssortHelper.cs b/Libraries/SPTarkov.Server.Core/Helpers/AssortHelper.cs
index 5ca8c838..8036f34a 100644
--- a/Libraries/SPTarkov.Server.Core/Helpers/AssortHelper.cs
+++ b/Libraries/SPTarkov.Server.Core/Helpers/AssortHelper.cs
@@ -28,7 +28,7 @@ public class AssortHelper(
         PmcData pmcProfile,
         MongoId traderId,
         TraderAssort traderAssorts,
-        Dictionary<string, Dictionary<string, string>> mergedQuestAssorts,
+        Dictionary<string, Dictionary<MongoId, string>> mergedQuestAssorts,
         bool isFlea = false
     )
     {
@@ -71,15 +71,15 @@ public class AssortHelper(
     /// <param name="mergedQuestAssorts">quest assorts to search for assort id</param>
     /// <param name="assortId">Assort to look for linked quest id</param>
     /// <returns>quest id + array of quest status the assort should show for</returns>
-    protected KeyValuePair<string, List<QuestStatusEnum>>? GetQuestIdAndStatusThatShowAssort(
-        Dictionary<string, Dictionary<string, string>> mergedQuestAssorts,
-        string assortId
+    protected KeyValuePair<MongoId, HashSet<QuestStatusEnum>>? GetQuestIdAndStatusThatShowAssort(
+        Dictionary<string, Dictionary<MongoId, string>> mergedQuestAssorts,
+        MongoId assortId
     )
     {
         if (mergedQuestAssorts.TryGetValue("started", out var dict1) && dict1.ContainsKey(assortId))
         // Assort unlocked by starting quest, assort is visible to player when : started or ready to hand in + handed in
         {
-            return new KeyValuePair<string, List<QuestStatusEnum>>(
+            return new KeyValuePair<MongoId, HashSet<QuestStatusEnum>>(
                 mergedQuestAssorts["started"][assortId],
                 [
                     QuestStatusEnum.Started,
@@ -91,7 +91,7 @@ public class AssortHelper(
 
         if (mergedQuestAssorts.TryGetValue("success", out var dict2) && dict2.ContainsKey(assortId))
         {
-            return new KeyValuePair<string, List<QuestStatusEnum>>(
+            return new KeyValuePair<MongoId, HashSet<QuestStatusEnum>>(
                 mergedQuestAssorts["success"][assortId],
                 [QuestStatusEnum.Success]
             );
@@ -99,7 +99,7 @@ public class AssortHelper(
 
         if (mergedQuestAssorts.TryGetValue("fail", out var dict3) && dict3.ContainsKey(assortId))
         {
-            return new KeyValuePair<string, List<QuestStatusEnum>>(
+            return new KeyValuePair<MongoId, HashSet<QuestStatusEnum>>(
                 mergedQuestAssorts["fail"][assortId],
                 [QuestStatusEnum.Fail]
             );
diff --git a/Libraries/SPTarkov.Server.Core/Helpers/BotGeneratorHelper.cs b/Libraries/SPTarkov.Server.Core/Helpers/BotGeneratorHelper.cs
index a765f2c5..f07b4f94 100644
--- a/Libraries/SPTarkov.Server.Core/Helpers/BotGeneratorHelper.cs
+++ b/Libraries/SPTarkov.Server.Core/Helpers/BotGeneratorHelper.cs
@@ -37,7 +37,7 @@ public class BotGeneratorHelper(
         nameof(EquipmentSlots.ArmBand),
     ];
 
-    private static readonly string[] _pmcTypes =
+    private static readonly FrozenSet<string> _pmcTypes =
     [
         Sides.PmcBear.ToLowerInvariant(),
         Sides.PmcUsec.ToLowerInvariant(),
@@ -524,9 +524,7 @@ public class BotGeneratorHelper(
     /// <returns>Equipment role (e.g. pmc / assault / bossTagilla)</returns>
     public string GetBotEquipmentRole(string botRole)
     {
-        return _pmcTypes.Contains(botRole, StringComparer.OrdinalIgnoreCase)
-            ? Sides.PmcEquipmentRole
-            : botRole;
+        return _pmcTypes.Contains(botRole.ToLower()) ? Sides.PmcEquipmentRole : botRole;
     }
 
     /// <summary>
@@ -775,13 +773,13 @@ public class BotGeneratorHelper(
             return false;
         }
 
-        // If Filter array only contains 1 filter and its for basetype 'item', allow it
+        // If Filter array only contains 1 filter and it is for basetype 'item', allow it
         if (filter.Count == 1 && filter.Contains(BaseClasses.ITEM))
         {
             return true;
         }
 
-        // If allowed filter has something in it + filter doesnt have basetype 'item', not allowed
+        // If allowed filter has something in it + filter doesn't have basetype 'item', not allowed
         if (filter.Count > 0 && !filter.Contains(itemDetails?.Parent ?? string.Empty))
         {
             return false;
diff --git a/Libraries/SPTarkov.Server.Core/Helpers/BotHelper.cs b/Libraries/SPTarkov.Server.Core/Helpers/BotHelper.cs
index c5cd8588..d28a08d9 100644
--- a/Libraries/SPTarkov.Server.Core/Helpers/BotHelper.cs
+++ b/Libraries/SPTarkov.Server.Core/Helpers/BotHelper.cs
@@ -126,21 +126,6 @@ public class BotHelper(
         }
     }
 
-    /// <summary>
-    ///     is the provided role a PMC, case-agnostic
-    /// </summary>
-    /// <param name="botRole">Role to check</param>
-    /// <returns>True if role is PMC</returns>
-    public bool BotRoleIsPmc(string botRole)
-    {
-        HashSet<string> listToCheck =
-        [
-            _pmcConfig.UsecType.ToLowerInvariant(),
-            _pmcConfig.BearType.ToLowerInvariant(),
-        ];
-        return listToCheck.Contains(botRole.ToLowerInvariant());
-    }
-
     /// <summary>
     ///     Get randomization settings for bot from config/bot.json
     /// </summary>
diff --git a/Libraries/SPTarkov.Server.Core/Helpers/InRaidHelper.cs b/Libraries/SPTarkov.Server.Core/Helpers/InRaidHelper.cs
index 337d52ee..ff2427dc 100644
--- a/Libraries/SPTarkov.Server.Core/Helpers/InRaidHelper.cs
+++ b/Libraries/SPTarkov.Server.Core/Helpers/InRaidHelper.cs
@@ -250,7 +250,7 @@ public class InRaidHelper(
             // Ensure we don't pick up pocket items from mannequins
             if (
                 item.SlotId.StartsWith("pocket")
-                && pmcProfile.DoesItemHaveRootId(item, pmcProfile.Inventory.Equipment)
+                && pmcProfile.DoesItemHaveRootId(item, pmcProfile.Inventory.Equipment.Value)
             )
             {
                 return true;
diff --git a/Libraries/SPTarkov.Server.Core/Helpers/ItemHelper.cs b/Libraries/SPTarkov.Server.Core/Helpers/ItemHelper.cs
index 2db00564..f1a2de5b 100644
--- a/Libraries/SPTarkov.Server.Core/Helpers/ItemHelper.cs
+++ b/Libraries/SPTarkov.Server.Core/Helpers/ItemHelper.cs
@@ -1152,7 +1152,7 @@ public class ItemHelper(
     /// <param name="tpl">Items tpl to check parents of</param>
     /// <param name="tplsToCheck">Tpl values to check if parents of item match</param>
     /// <returns>bool Match found</returns>
-    public bool DoesItemOrParentsIdMatch(MongoId tpl, List<MongoId> tplsToCheck)
+    public bool DoesItemOrParentsIdMatch(MongoId tpl, HashSet<MongoId> tplsToCheck)
     {
         var (itemExists, item) = GetItem(tpl);
 
@@ -1631,7 +1631,7 @@ public class ItemHelper(
         string caliber,
         Dictionary<string, IEnumerable<StaticAmmoDetails>> staticAmmoDist,
         MongoId? fallbackCartridgeTpl = null,
-        ICollection<MongoId>? cartridgeWhitelist = null
+        ISet<MongoId>? cartridgeWhitelist = null
     )
     {
         var ammos = staticAmmoDist.GetValueOrDefault(caliber, []);
diff --git a/Libraries/SPTarkov.Server.Core/Helpers/ProfileHelper.cs b/Libraries/SPTarkov.Server.Core/Helpers/ProfileHelper.cs
index 338e4b61..1009532c 100644
--- a/Libraries/SPTarkov.Server.Core/Helpers/ProfileHelper.cs
+++ b/Libraries/SPTarkov.Server.Core/Helpers/ProfileHelper.cs
@@ -372,13 +372,13 @@ public class ProfileHelper(
         var secureContainer = items.FirstOrDefault(i => i.SlotId == "SecuredContainer");
         if (secureContainer is not null)
         {
-            // Find and remove container + children
-            var childItemsInSecureContainer = items.GetItemWithChildrenTpls(secureContainer.Id);
+            // Find secure container + children
+            var secureContainerAndChildrenIds = items
+                .GetItemWithChildrenTpls(secureContainer.Id)
+                .ToHashSet();
 
-            // Remove child items + secure container
-            profile.Inventory.Items = items
-                .Where(i => !childItemsInSecureContainer.Contains(i.Id))
-                .ToList();
+            // Remove secure container + its children
+            items.RemoveAll(x => secureContainerAndChildrenIds.Contains(x.Id));
         }
 
         return profile;
diff --git a/Libraries/SPTarkov.Server.Core/Helpers/QuestHelper.cs b/Libraries/SPTarkov.Server.Core/Helpers/QuestHelper.cs
index a5e411f9..2756cf36 100644
--- a/Libraries/SPTarkov.Server.Core/Helpers/QuestHelper.cs
+++ b/Libraries/SPTarkov.Server.Core/Helpers/QuestHelper.cs
@@ -103,7 +103,7 @@ public class QuestHelper(
     /// <param name="before">List of quests #1</param>
     /// <param name="after">List of quests #2</param>
     /// <returns>quests not in before</returns>
-    public List<Quest> GetDeltaQuests(List<Quest> before, List<Quest> after)
+    public IEnumerable<Quest> GetDeltaQuests(List<Quest> before, List<Quest> after)
     {
         // Nothing to compare against, return after
         if (before.Count == 0)
@@ -115,7 +115,7 @@ public class QuestHelper(
         var beforeQuests = before.Select(quest => quest.Id).ToHashSet();
 
         // Return quests found in after but not before
-        return after.Where(quest => !beforeQuests.Contains(quest.Id)).ToList();
+        return after.Where(quest => !beforeQuests.Contains(quest.Id));
     }
 
     /// <summary>
@@ -586,7 +586,7 @@ public class QuestHelper(
                 var acceptedQuestCondition = q.Conditions.AvailableForStart.FirstOrDefault(c =>
                     c.ConditionType == "Quest"
                     && (c.Target.IsList ? c.Target.List : [c.Target.Item]).Contains(failedQuestId)
-                    && c.Status[0] == QuestStatusEnum.Fail
+                    && c.Status.First() == QuestStatusEnum.Fail
                 );
 
                 if (acceptedQuestCondition is null)
@@ -1586,7 +1586,7 @@ public class QuestHelper(
     /// <param name="completedQuestId">Quest just completed</param>
     protected void AddTimeLockedQuestsToProfile(
         PmcData pmcData,
-        List<Quest> quests,
+        IEnumerable<Quest> quests,
         MongoId completedQuestId
     )
     {
diff --git a/Libraries/SPTarkov.Server.Core/Helpers/RagfairOfferHelper.cs b/Libraries/SPTarkov.Server.Core/Helpers/RagfairOfferHelper.cs
index 864fd40b..d69e082c 100644
--- a/Libraries/SPTarkov.Server.Core/Helpers/RagfairOfferHelper.cs
+++ b/Libraries/SPTarkov.Server.Core/Helpers/RagfairOfferHelper.cs
@@ -612,9 +612,9 @@ public class RagfairOfferHelper(
         return false;
     }
 
-    protected HashSet<string> GetLoyaltyLockedOffers(List<RagfairOffer> offers, PmcData pmcProfile)
+    protected HashSet<MongoId> GetLoyaltyLockedOffers(List<RagfairOffer> offers, PmcData pmcProfile)
     {
-        var loyaltyLockedOffers = new HashSet<string>();
+        var loyaltyLockedOffers = new HashSet<MongoId>();
         foreach (var offer in offers.Where(x => x.IsTraderOffer()))
         {
             if (
diff --git a/Libraries/SPTarkov.Server.Core/Helpers/TraderAssortHelper.cs b/Libraries/SPTarkov.Server.Core/Helpers/TraderAssortHelper.cs
index a6022730..d3086c61 100644
--- a/Libraries/SPTarkov.Server.Core/Helpers/TraderAssortHelper.cs
+++ b/Libraries/SPTarkov.Server.Core/Helpers/TraderAssortHelper.cs
@@ -24,8 +24,8 @@ public class TraderAssortHelper(
     ICloner cloner
 )
 {
-    private Dictionary<string, Dictionary<string, string>>? _mergedQuestAssorts;
-    protected virtual Dictionary<string, Dictionary<string, string>> MergedQuestAssorts
+    private Dictionary<string, Dictionary<MongoId, string>>? _mergedQuestAssorts;
+    protected virtual Dictionary<string, Dictionary<MongoId, string>> MergedQuestAssorts
     {
         get { return _mergedQuestAssorts ??= HydrateMergedQuestAssorts(); }
     }
@@ -148,9 +148,9 @@ public class TraderAssortHelper(
     /// Create a dictionary keyed by quest status (started/success) with every assortId to QuestId from every trader
     /// </summary>
     /// <returns>Dictionary</returns>
-    protected Dictionary<string, Dictionary<string, string>> HydrateMergedQuestAssorts()
+    protected Dictionary<string, Dictionary<MongoId, string>> HydrateMergedQuestAssorts()
     {
-        var result = new Dictionary<string, Dictionary<string, string>>();
+        var result = new Dictionary<string, Dictionary<MongoId, string>>();
 
         // Loop every trader
         var traders = databaseService.GetTraders();
@@ -171,7 +171,7 @@ public class TraderAssortHelper(
                 }
 
                 // Null guard - ensure Started/Success/fail exists
-                result.TryAdd(unlockStatus, new Dictionary<string, string>());
+                result.TryAdd(unlockStatus, new Dictionary<MongoId, string>());
 
                 foreach (var (assortId, questId) in assortToQuestDict)
                 {
diff --git a/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/BotBase.cs b/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/BotBase.cs
index ad6e7f0c..9cb5a530 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/BotBase.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/BotBase.cs
@@ -606,7 +606,7 @@ public record CounterKeyValue
     [JsonExtensionData]
     public Dictionary<string, object>? ExtensionData { get; set; }
 
-    public IEnumerable<string>? Key { get; set; }
+    public HashSet<string>? Key { get; set; }
 
     public double? Value { get; set; }
 }
diff --git a/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/ProfileTemplate.cs b/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/ProfileTemplate.cs
index bb99af27..87f79f30 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/ProfileTemplate.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/ProfileTemplate.cs
@@ -79,11 +79,11 @@ public record ProfileTraderTemplate
     ///     What traders default to being locked on profile creation
     /// </summary>
     [JsonPropertyName("lockedByDefaultOverride")]
-    public List<MongoId>? LockedByDefaultOverride { get; set; }
+    public HashSet<MongoId>? LockedByDefaultOverride { get; set; }
 
     /// <summary>
     ///     What traders should have their clothing unlocked/purchased on creation
     /// </summary>
     [JsonPropertyName("purchaseAllClothingByDefaultForTrader")]
-    public List<MongoId>? PurchaseAllClothingByDefaultForTrader { get; set; }
+    public HashSet<MongoId>? PurchaseAllClothingByDefaultForTrader { get; set; }
 }
diff --git a/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/Quest.cs b/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/Quest.cs
index f0d7d1ec..20f42673 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/Quest.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/Quest.cs
@@ -213,7 +213,7 @@ public record QuestCondition
     public string? Type { get; set; }
 
     [JsonPropertyName("status")]
-    public List<QuestStatusEnum>? Status { get; set; }
+    public HashSet<QuestStatusEnum>? Status { get; set; }
 
     [JsonPropertyName("availableAfter")]
     public int? AvailableAfter { get; set; }
diff --git a/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/RepeatableQuests.cs b/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/RepeatableQuests.cs
index 19972015..2e06d406 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/RepeatableQuests.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/RepeatableQuests.cs
@@ -189,7 +189,7 @@ public record ItemsBlacklist
     public int? MinPlayerLevel { get; set; }
 
     [JsonPropertyName("itemIds")]
-    public List<string>? ItemIds { get; set; }
+    public HashSet<MongoId>? ItemIds { get; set; }
 }
 
 public record ItemsWhitelist
@@ -201,7 +201,7 @@ public record ItemsWhitelist
     public int? MinPlayerLevel { get; set; }
 
     [JsonPropertyName("itemIds")]
-    public List<string>? ItemIds { get; set; }
+    public HashSet<MongoId>? ItemIds { get; set; }
 }
 
 public record SampleQuests
diff --git a/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/TemplateItem.cs b/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/TemplateItem.cs
index 9557ed4b..4f327362 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/TemplateItem.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Eft/Common/Tables/TemplateItem.cs
@@ -1725,7 +1725,7 @@ public record GridFilter
     public HashSet<string>? Filter { get; set; }
 
     [JsonPropertyName("ExcludedFilter")]
-    public List<string>? ExcludedFilter { get; set; }
+    public HashSet<string>? ExcludedFilter { get; set; }
 
     [JsonPropertyName("locked")]
     public bool? Locked { get; set; }
diff --git a/Libraries/SPTarkov.Server.Core/Models/Eft/Profile/SptProfile.cs b/Libraries/SPTarkov.Server.Core/Models/Eft/Profile/SptProfile.cs
index e5a11bd6..55606b89 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Eft/Profile/SptProfile.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Eft/Profile/SptProfile.cs
@@ -57,7 +57,7 @@ public record SptProfile
     ///     List of friend profile IDs
     /// </summary>
     [JsonPropertyName("friends")]
-    public List<MongoId>? FriendProfileIds { get; set; }
+    public HashSet<MongoId>? FriendProfileIds { get; set; }
 
     /// <summary>
     ///     Stores profile-related customisation, e.g. clothing / hideout walls / floors
@@ -422,7 +422,7 @@ public record Spt
     ///     item TPLs blacklisted from being sold on flea for this profile
     /// </summary>
     [JsonPropertyName("blacklistedItemTpls")]
-    public HashSet<string>? BlacklistedItemTemplates { get; set; }
+    public HashSet<MongoId>? BlacklistedItemTemplates { get; set; }
 
     /// <summary>
     ///     key: daily type
diff --git a/Libraries/SPTarkov.Server.Core/Models/Spt/Bots/GenerateEquipmentProperties.cs b/Libraries/SPTarkov.Server.Core/Models/Spt/Bots/GenerateEquipmentProperties.cs
index b98065e2..de0e8b08 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Spt/Bots/GenerateEquipmentProperties.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Spt/Bots/GenerateEquipmentProperties.cs
@@ -54,7 +54,7 @@ public record GenerateEquipmentProperties
     ///     OPTIONAL - Do not generate mods for tpls in this array
     /// </summary>
     [JsonPropertyName("generateModsBlacklist")]
-    public HashSet<string>? GenerateModsBlacklist { get; set; }
+    public HashSet<MongoId>? GenerateModsBlacklist { get; set; }
 
     [JsonPropertyName("generatingPlayerLevel")]
     public double? GeneratingPlayerLevel { get; set; }
diff --git a/Libraries/SPTarkov.Server.Core/Models/Spt/Bots/ModToSpawnRequest.cs b/Libraries/SPTarkov.Server.Core/Models/Spt/Bots/ModToSpawnRequest.cs
index 9ade62a7..74aa919e 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Spt/Bots/ModToSpawnRequest.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Spt/Bots/ModToSpawnRequest.cs
@@ -30,7 +30,7 @@ public record ModToSpawnRequest
     ///     Parent slot the item will be a part of
     /// </summary>
     [JsonPropertyName("botWeaponSightWhitelist")]
-    public Dictionary<MongoId, List<MongoId>>? BotWeaponSightWhitelist { get; set; }
+    public Dictionary<MongoId, HashSet<MongoId>>? BotWeaponSightWhitelist { get; set; }
 
     /// <summary>
     ///     Blacklist to prevent mods from being picked
diff --git a/Libraries/SPTarkov.Server.Core/Models/Spt/Config/AirdropConfig.cs b/Libraries/SPTarkov.Server.Core/Models/Spt/Config/AirdropConfig.cs
index 683b3c39..52fcf68e 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Spt/Config/AirdropConfig.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Spt/Config/AirdropConfig.cs
@@ -86,7 +86,7 @@ public record AirdropLoot
     ///     Armor levels to allow inside crate e.g. [4,5,6]
     /// </summary>
     [JsonPropertyName("armorLevelWhitelist")]
-    public List<int>? ArmorLevelWhitelist { get; set; }
+    public HashSet<int>? ArmorLevelWhitelist { get; set; }
 
     /// <summary>
     ///     Should boss items be added to airdrop crate
diff --git a/Libraries/SPTarkov.Server.Core/Models/Spt/Config/BotConfig.cs b/Libraries/SPTarkov.Server.Core/Models/Spt/Config/BotConfig.cs
index 90cd9104..9f346544 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Spt/Config/BotConfig.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Spt/Config/BotConfig.cs
@@ -188,7 +188,7 @@ public record WalletLootSettings
     ///     What wallets will have money in them
     /// </summary>
     [JsonPropertyName("walletTplPool")]
-    public required List<MongoId> WalletTplPool { get; set; }
+    public required HashSet<MongoId> WalletTplPool { get; set; }
 }
 
 public record EquipmentFilters
@@ -206,7 +206,7 @@ public record EquipmentFilters
     ///     Whitelist for weapon sight types allowed per gun
     /// </summary>
     [JsonPropertyName("weaponSightWhitelist")]
-    public Dictionary<MongoId, List<MongoId>>? WeaponSightWhitelist { get; set; }
+    public Dictionary<MongoId, HashSet<MongoId>>? WeaponSightWhitelist { get; set; }
 
     [JsonPropertyName("forceOnlyArmoredRigWhenNoArmor")]
     public bool? ForceOnlyArmoredRigWhenNoArmor { get; set; }
@@ -332,13 +332,13 @@ public record RandomisationDetails
     ///     Mod slots that should be fully randomised -ignores mods from bottype.json and instead creates a pool using items.json
     /// </summary>
     [JsonPropertyName("randomisedWeaponModSlots")]
-    public List<string>? RandomisedWeaponModSlots { get; set; }
+    public HashSet<string>? RandomisedWeaponModSlots { get; set; }
 
     /// <summary>
     ///     Armor slots that should be randomised e.g. 'Headwear, Armband'
     /// </summary>
     [JsonPropertyName("randomisedArmorSlots")]
-    public List<string>? RandomisedArmorSlots { get; set; }
+    public HashSet<string>? RandomisedArmorSlots { get; set; }
 
     /// <summary>
     ///     Equipment chances
diff --git a/Libraries/SPTarkov.Server.Core/Models/Spt/Config/InRaidConfig.cs b/Libraries/SPTarkov.Server.Core/Models/Spt/Config/InRaidConfig.cs
index bb695cd0..0bee35de 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Spt/Config/InRaidConfig.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Spt/Config/InRaidConfig.cs
@@ -17,13 +17,13 @@ public record InRaidConfig : BaseConfig
     ///     Names of car extracts
     /// </summary>
     [JsonPropertyName("carExtracts")]
-    public required List<string> CarExtracts { get; set; }
+    public required HashSet<string> CarExtracts { get; set; }
 
     /// <summary>
     ///     Names of coop extracts
     /// </summary>
     [JsonPropertyName("coopExtracts")]
-    public required List<string> CoopExtracts { get; set; }
+    public required HashSet<string> CoopExtracts { get; set; }
 
     /// <summary>
     ///     Fence rep gain from a single car extract
diff --git a/Libraries/SPTarkov.Server.Core/Models/Spt/Config/LocaleConfig.cs b/Libraries/SPTarkov.Server.Core/Models/Spt/Config/LocaleConfig.cs
index 9a2cabf7..1b4aa481 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Spt/Config/LocaleConfig.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Spt/Config/LocaleConfig.cs
@@ -23,7 +23,7 @@ public record LocaleConfig : BaseConfig
     ///     Languages server can be translated into
     /// </summary>
     [JsonPropertyName("serverSupportedLocales")]
-    public required List<string> ServerSupportedLocales { get; set; }
+    public required HashSet<string> ServerSupportedLocales { get; set; }
 
     [JsonPropertyName("fallbacks")]
     public required Dictionary<string, string> Fallbacks { get; set; }
diff --git a/Libraries/SPTarkov.Server.Core/Models/Spt/Config/LocationConfig.cs b/Libraries/SPTarkov.Server.Core/Models/Spt/Config/LocationConfig.cs
index cb6e3ee2..4b6452f9 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Spt/Config/LocationConfig.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Spt/Config/LocationConfig.cs
@@ -106,7 +106,7 @@ public record LocationConfig : BaseConfig
     ///     Key: map, value: loose loot ids to ignore
     /// </summary>
     [JsonPropertyName("looseLootBlacklist")]
-    public required Dictionary<string, List<string>> LooseLootBlacklist { get; set; }
+    public required Dictionary<string, HashSet<string>> LooseLootBlacklist { get; set; }
 
     /// <summary>
     ///     Key: map, value: settings to control how long scav raids are
diff --git a/Libraries/SPTarkov.Server.Core/Models/Spt/Config/QuestConfig.cs b/Libraries/SPTarkov.Server.Core/Models/Spt/Config/QuestConfig.cs
index e51703e3..f2098c8a 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Spt/Config/QuestConfig.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Spt/Config/QuestConfig.cs
@@ -413,7 +413,7 @@ public record SpecificExits
     ///     Whitelist of specific extract types
     /// </summary>
     [JsonPropertyName("passageRequirementWhitelist")]
-    public required List<string> PassageRequirementWhitelist { get; set; }
+    public required HashSet<string> PassageRequirementWhitelist { get; set; }
 }
 
 public record Completion : BaseQuestConfig
@@ -541,7 +541,7 @@ public record EliminationConfig : BaseQuestConfig
     ///     Locations that should be blacklisted as a requirement
     /// </summary>
     [JsonPropertyName("distLocationBlacklist")]
-    public required List<string> DistLocationBlacklist { get; set; }
+    public required HashSet<string> DistLocationBlacklist { get; set; }
 
     /// <summary>
     ///     Probability that a distance requirement is chosen
diff --git a/Libraries/SPTarkov.Server.Core/Models/Spt/Config/SeasonalEventConfig.cs b/Libraries/SPTarkov.Server.Core/Models/Spt/Config/SeasonalEventConfig.cs
index d399da1d..d432051a 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Spt/Config/SeasonalEventConfig.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Spt/Config/SeasonalEventConfig.cs
@@ -63,7 +63,7 @@ public record SeasonalEventConfig : BaseConfig
     ///     Ids of containers on locations that only have Christmas loot
     /// </summary>
     [JsonPropertyName("christmasContainerIds")]
-    public required List<string> ChristmasContainerIds { get; set; }
+    public required HashSet<string> ChristmasContainerIds { get; set; }
 
     /// <summary>
     ///     Season - botType - location (body/feet/hands/head)
diff --git a/Libraries/SPTarkov.Server.Core/Models/Spt/Services/LootRequest.cs b/Libraries/SPTarkov.Server.Core/Models/Spt/Services/LootRequest.cs
index e5864c65..ca707507 100644
--- a/Libraries/SPTarkov.Server.Core/Models/Spt/Services/LootRequest.cs
+++ b/Libraries/SPTarkov.Server.Core/Models/Spt/Services/LootRequest.cs
@@ -58,7 +58,7 @@ public record LootRequest
     ///     Allowed armor plate levels 2/3/4/5/6 for armor generated
     /// </summary>
     [JsonPropertyName("armorLevelWhitelist")]
-    public List<int>? ArmorLevelWhitelist { get; set; }
+    public HashSet<int>? ArmorLevelWhitelist { get; set; }
 
     /// <summary>
     ///     Should boss items be included in allowed items
diff --git a/Libraries/SPTarkov.Server.Core/Services/BotEquipmentFilterService.cs b/Libraries/SPTarkov.Server.Core/Services/BotEquipmentFilterService.cs
index 66002719..bcf03405 100644
--- a/Libraries/SPTarkov.Server.Core/Services/BotEquipmentFilterService.cs
+++ b/Libraries/SPTarkov.Server.Core/Services/BotEquipmentFilterService.cs
@@ -161,16 +161,13 @@ public class BotEquipmentFilterService(
     /// </summary>
     /// <param name="botEquipmentRole">equipment role of bot to look up</param>
     /// <returns>Dictionary of weapon type and their whitelisted scope types</returns>
-    public Dictionary<MongoId, List<MongoId>> GetBotWeaponSightWhitelist(string botEquipmentRole)
+    public Dictionary<MongoId, HashSet<MongoId>>? GetBotWeaponSightWhitelist(
+        string botEquipmentRole
+    )
     {
-        var botEquipmentSettings = _botConfig.Equipment[botEquipmentRole];
-
-        if (botEquipmentSettings is null)
-        {
-            return null;
-        }
-
-        return botEquipmentSettings.WeaponSightWhitelist;
+        return _botConfig.Equipment.TryGetValue(botEquipmentRole, out var botEquipmentSettings)
+            ? botEquipmentSettings.WeaponSightWhitelist
+            : null;
     }
 
     /// <summary>
diff --git a/Libraries/SPTarkov.Server.Core/Services/BtrDeliveryService.cs b/Libraries/SPTarkov.Server.Core/Services/BtrDeliveryService.cs
index b661258d..3f81bee0 100644
--- a/Libraries/SPTarkov.Server.Core/Services/BtrDeliveryService.cs
+++ b/Libraries/SPTarkov.Server.Core/Services/BtrDeliveryService.cs
@@ -66,7 +66,7 @@ public class BtrDeliveryService(
 
         // Remove any items that were returned by the item delivery, but also insured, from the player's insurance list
         // This is to stop items being duplicated by being returned from both item delivery and insurance
-        var deliveredItemIds = items.Select(item => item.Id);
+        var deliveredItemIds = items.Select(item => item.Id).ToHashSet();
         pmcData.InsuredItems = pmcData
             .InsuredItems.Where(insuredItem => !deliveredItemIds.Contains(insuredItem.ItemId.Value))
             .ToList();
diff --git a/Libraries/SPTarkov.Server.Core/Services/CircleOfCultistService.cs b/Libraries/SPTarkov.Server.Core/Services/CircleOfCultistService.cs
index 8a1eaaef..6f502502 100644
--- a/Libraries/SPTarkov.Server.Core/Services/CircleOfCultistService.cs
+++ b/Libraries/SPTarkov.Server.Core/Services/CircleOfCultistService.cs
@@ -468,6 +468,7 @@ public class CircleOfCultistService(
         // Handle special case of tagilla helmets - only one reward is allowed
         if (directReward.Reward.Contains(ItemTpl.FACECOVER_TAGILLAS_WELDING_MASK_GORILLA))
         {
+            // TODO: this is likely redundant with direct reward system in config?
             directReward.Reward = [randomUtil.GetArrayValue(directReward.Reward)];
         }
 
@@ -598,7 +599,7 @@ public class CircleOfCultistService(
     /// </summary>
     /// <param name="rewardTpl">Item being rewarded to get stack size of</param>
     /// <returns>stack size of item</returns>
-    protected int GetDirectRewardBaseTypeStackSize(string rewardTpl)
+    protected int GetDirectRewardBaseTypeStackSize(MongoId rewardTpl)
     {
         var itemDetails = itemHelper.GetItem(rewardTpl);
         if (!itemDetails.Key)
diff --git a/Libraries/SPTarkov.Server.Core/Services/LocaleService.cs b/Libraries/SPTarkov.Server.Core/Services/LocaleService.cs
index 893b2930..e4601833 100644
--- a/Libraries/SPTarkov.Server.Core/Services/LocaleService.cs
+++ b/Libraries/SPTarkov.Server.Core/Services/LocaleService.cs
@@ -109,7 +109,7 @@ public class LocaleService(
     ///     Get array of languages supported for localisation
     /// </summary>
     /// <returns> List of locales e.g. en/fr/cn </returns>
-    public List<string> GetServerSupportedLocales()
+    public HashSet<string> GetServerSupportedLocales()
     {
         return _localeConfig.ServerSupportedLocales;
     }
diff --git a/Libraries/SPTarkov.Server.Core/Services/LocationLifecycleService.cs b/Libraries/SPTarkov.Server.Core/Services/LocationLifecycleService.cs
index cf0d9c5f..0198689d 100644
--- a/Libraries/SPTarkov.Server.Core/Services/LocationLifecycleService.cs
+++ b/Libraries/SPTarkov.Server.Core/Services/LocationLifecycleService.cs
@@ -601,7 +601,7 @@ public class LocationLifecycleService(
     /// </summary>
     /// <param name="extractName"> Name of extract player took </param>
     /// <returns> True if coop extract </returns>
-    protected bool ExtractTakenWasCoop(string extractName)
+    protected bool ExtractTakenWasCoop(string? extractName)
     {
         // No extract name, not a coop extract
         if (extractName is null)
@@ -990,7 +990,8 @@ public class LocationLifecycleService(
                     is not QuestStatusEnum.AvailableForStart
                         and not QuestStatusEnum.Success
             )
-            .Select(status => status.QId);
+            .Select(status => status.QId)
+            .ToHashSet();
 
         // Get db details of quests we found above
         var questDb = databaseService
diff --git a/Libraries/SPTarkov.Server.Core/Services/OpenZoneService.cs b/Libraries/SPTarkov.Server.Core/Services/OpenZoneService.cs
index 226dd676..3f4b785a 100644
--- a/Libraries/SPTarkov.Server.Core/Services/OpenZoneService.cs
+++ b/Libraries/SPTarkov.Server.Core/Services/OpenZoneService.cs
@@ -53,7 +53,7 @@ public class OpenZoneService(
             var zonesToAdd = _locationConfig.OpenZones[mapKvP.Key];
 
             // Convert openzones string into list, easier to work wih
-            var mapOpenZonesArray = dbLocations[mapKvP.Key].Base.OpenZones.Split(",").ToList();
+            var mapOpenZonesArray = dbLocations[mapKvP.Key].Base.OpenZones.Split(",").ToHashSet();
             foreach (
                 var zoneToAdd in zonesToAdd.Where(zoneToAdd =>
                     !mapOpenZonesArray.Contains(zoneToAdd)
diff --git a/Libraries/SPTarkov.Server.Core/Services/ServerLocalisationService.cs b/Libraries/SPTarkov.Server.Core/Services/ServerLocalisationService.cs
index f7935493..ad86823b 100644
--- a/Libraries/SPTarkov.Server.Core/Services/ServerLocalisationService.cs
+++ b/Libraries/SPTarkov.Server.Core/Services/ServerLocalisationService.cs
@@ -131,9 +131,9 @@ public class ServerLocalisationService(
     /// <returns> Locale text </returns>
     public string GetRandomTextThatMatchesPartialKey(string partialKey)
     {
-        var matchingKeys = GetLocaleKeys().Where(x => x.Contains(partialKey)).ToList();
+        var matchingKeys = GetLocaleKeys().Where(x => x.Contains(partialKey));
 
-        if (matchingKeys.Count == 0)
+        if (!matchingKeys.Any())
         {
             logger.Warning($"No locale keys found for: {partialKey}");
 
diff --git a/Libraries/SPTarkov.Server.Core/Utils/RagfairOfferHolder.cs b/Libraries/SPTarkov.Server.Core/Utils/RagfairOfferHolder.cs
index c1ce526e..3be76693 100644
--- a/Libraries/SPTarkov.Server.Core/Utils/RagfairOfferHolder.cs
+++ b/Libraries/SPTarkov.Server.Core/Utils/RagfairOfferHolder.cs
@@ -21,7 +21,7 @@ public class RagfairOfferHolder(
     /// <summary>
     /// Expired offer Ids
     /// </summary>
-    private readonly HashSet<string> _expiredOfferIds = [];
+    private readonly HashSet<MongoId> _expiredOfferIds = [];
 
     /// <summary>
     /// Ragfair offer cache, keyed by offer Id
@@ -55,7 +55,7 @@ public class RagfairOfferHolder(
     ///     Get a ragfair offer by its id
     /// </summary>
     /// <returns>RagfairOffer</returns>
-    public HashSet<string> GetStaleOfferIds()
+    public HashSet<MongoId> GetStaleOfferIds()
     {
         lock (_expiredOfferIdsLock)
         {