First set up your characters and make sure that each character has the InventoryPlayer component attached.
Each InventoryPlayer component has references to the player’s inventories and character (equippable) collections.
Once the player is “selected” or “set” his/her inventories will be selected as the new "loot to collections". This means that when a new player is set all actions from the InventoryManager such as InventoryManager.AddItem() will apply to those new inventories.
Setting the current player can be done with 1 line of code:
InventoryPlayerManager.instance.currentPlayer = myPlayer; // Set the current player and auto. switch collections
It is also possible to share inventories between characters. This will not bind the collection to a specific player, and allow all your characters to use the inventory. This can be done by marking your inventory as Is shared collection.