Welcome to stackable backpacks! Where you can put a backpack inside a backpack!
How does it work?
Simple: You can't put backpacks A inside backpacks A, but you can put them inside a backpack B
So you can put a Backpack A inside a Backpack B, and a Backpack B inside that Backpack A.
Also, you can simply use it as a cool backpack mod.
Backpacks recipes:
Backpacks usage example: