I want to create a platform game with a 3 itens slots on the interface. These 3 slots allows the player can carrying a total of only 3 itens. Thus, if the player is already carrying a total of 3 itens, he needs to discard a item and then take that he wants (the discard could be by an automatic way - i.e: the discard is made from right to left. So, when the 3 slots are filled, the item that will be discarded is that one that occupies the first slot from the left).
The itens will distributed along the level design and an item discarded will be stay where it was left. When a item is collected, an icon representing it is added on the slot.
Each slot have a hotkey, which must pressed to "use" that item.
The idea is use the right item in the right place to progress in the game (a mix of adventure and platform game). I am searching for information that could help me to figure out how I can create this item system, but I can't find anything.