Not something I think can likely be achieved but I was wondering if there was any way to have a character start a game equipped with an item. My reason for asking is that the custom item I have is a backpack and I'd like it to function much like the vanilla backpack where characters can't keep the item in their inventory as to avoid abusing its extra inventory slots. However because it can't be stored in inventory, the character won't actually start with the item.
If this isn't possible, I'd then ask if it's possible to script a way for a player to only keep one of said item in their inventory.