Backpacks will replace the player's main inventory slots. Without wearing a backpack, you will only be able to store items in your hotbar.

As a bonus, backpacks will have their own individual inventories, meaning you can have multiple backpacks in your hotbar, and switch between them. You will not be able to nest backpacks within other backpacks, however.

Backpacks will have a dedicated slot in the player's inventory, above the offhand item slot.

Decided not to implement this