struct IInventory : public IGameObjectExtension {
  enum EInventorySlots {
    eInventorySlot_Weapon = 0,
    eInventorySlot_Explosives,
    eInventorySlot_Grenades,
    eInventorySlot_Special,
    eInventorySlot_Last
  };
};

IItemSystem.h

enum EInventorySlots {
  eInventorySlot_Weapon = 0,
  eInventorySlot_Explosives,
  eInventorySlot_Grenades,
  eInventorySlot_Special,
  eInventorySlot_Last
};

IItemSystem.h

virtual bool AddAccessory(IEntityClass* itemClass) = 0;

virtual void AddAmmoUser(IEntityClass* pAmmoType) = 0;

virtual bool AddItem(EntityId id) = 0;

virtual void AddListener(struct IInventoryListener* pListener) = 0;

virtual bool AreItemsInSameSlot(const char* itemClass1, const char* itemClass2) const = 0;

virtual void AssociateItemCategoryToSlot(const char* itemCategory, EInventorySlots slotId) = 0;

virtual void Clear() = 0;

virtual void Destroy() = 0;

virtual int FindItem(EntityId itemId) const = 0;

virtual int FindNext(IEntityClass * pClass, const char * category, int firstSlot, bool wrap) const = 0;

virtual int FindPrev(IEntityClass * pClass, const char * category, int firstSlot, bool wrap) const = 0;

virtual const char* GetAccessory(int slotId) const = 0;

virtual const IEntityClass* GetAccessoryClass(int slotId) const = 0;

virtual int GetAccessoryCount() const = 0;

virtual IActor* GetActor() = 0;

virtual int GetAmmoCapacity(IEntityClass* pAmmoType) const = 0;

virtual int GetAmmoCount(IEntityClass* pAmmoType) const = 0;

virtual IEntityClass* GetAmmoType(int idx) const = 0;

virtual int GetAmmoTypesCount() const = 0;

virtual int GetCapacity() const = 0;

virtual int GetCount() const = 0;

virtual int GetCountOfCategory(const char * categoryName) const = 0;

virtual int GetCountOfClass(const char * className) const = 0;

virtual int GetCountOfUniqueId(uint8 uniqueId) const = 0;

virtual EntityId GetCurrentItem() const = 0;

virtual EntityId GetHolsteredItem() const = 0;

virtual EntityId GetItem(int slotId) const = 0;

virtual EntityId GetItemByClass(IEntityClass * pClass, IItem * pIgnoreItem = NULL) const = 0;

virtual IItem* GetItemByName(const char* name) const = 0;

virtual const char* GetItemString(int slotId) const = 0;

virtual EntityId GetLastItem() const = 0;

virtual EntityId GetLastSelectedInSlot(IInventory::EInventorySlots slotId) const = 0;

virtual int GetNumberOfUsersForAmmo(IEntityClass* pAmmoType) const = 0;

virtual int GetSlotCount(int slotId) const = 0;

virtual EInventorySlots GetSlotForItemCategory(const char* itemCategory) const = 0;

virtual bool HasAccessory(IEntityClass* pClass) const = 0;

virtual void HolsterItem(bool holster) = 0;

virtual void IgnoreNextClear() = 0;

virtual bool IsAvailableSlotForItemCategory(const char* itemCategory) const = 0;

virtual bool IsAvailableSlotForItemClass(const char* itemClass) const = 0;

virtual bool IsSerializingForLevelChange() const = 0;

virtual void RemoveAllItems() = 0;

virtual void RemoveAmmoUser(IEntityClass* pAmmoType) = 0;

virtual bool RemoveItem(EntityId id) = 0;

virtual void RemoveListener(struct IInventoryListener* pListener) = 0;

virtual void ResetAmmo() = 0;

virtual void RMIReqToServer_AddEquipmentPack(const char* _pszEquipmentPack, bool _bAdd, bool _bPrimary) const = 0;

virtual void RMIReqToServer_AddItem(const char* _pszItemClass) const = 0;

virtual void RMIReqToServer_RemoveAllItems() const = 0;

virtual void RMIReqToServer_RemoveItem(const char* _pszItemClass) const = 0;

virtual void RMIReqToServer_SetAmmoCount(const char* _pszAmmoClass, int _iAmount) const = 0;

virtual void SerializeInventoryForLevelChange(TSerialize ser) = 0;

virtual void SetAmmoCapacity(IEntityClass* pAmmoType, int max) = 0;

virtual void SetAmmoCount(IEntityClass* pAmmoType, int count) = 0;

virtual void SetCurrentItem(EntityId itemId) = 0;

virtual void SetHolsteredItem(EntityId itemId) = 0;

virtual void SetInventorySlotCapacity(EInventorySlots slotId, unsigned int capacity) = 0;

virtual void SetLastItem(EntityId itemId) = 0;