Backpacks are the newest item added to Fortnite, with jetpacks being the first addition and enable players to hover and reach bigger heights.
The backpack items take up one slot in a player’s inventory and you can only can one at a time.
Backpacks are different from Back Blings as they cannot be bought in the Fortnite Item Shop as a cosmetic, but rather found in the game. Finding a Backpack item in Fortnite Battle Royale will take up an inventory slot and can be moved, the same as weapons and consumables and there will be a variety of uses for the different Backpack items. Players will not be able to carry more than one Backpack item at a time and when picking up a new Backpack item, it will automatically drop the item that is currently equipped by the player.
Once players equip the Backpack item, it will replace the Back Bling cosmetic players have, however the Back Bling will return when the Backpack item is no longer equipped. There will be some Backpack items in the future that will destroyed automatically when it had been fully consumed.
Here are the backpack details shared by Epic Games:
Backpacks take an inventory slot (like weapons & consumables) and can be moved to different positions.
Only one Backpack can be carried at a time.
If you pick up a different Backpack, it will be automatically swapped with the one currently equipped.
When a Backpack is fully consumed, it will be automatically destroyed.
While a Backpack is equipped, your Back Bling cosmetics will be hidden.
Back Bling will be reapplied when the Backpack is no longer equipped.