You craft a backpack like a chest but with leather instead of wood.
For a big backpack use tanned leather instead of normal leather.
Backpacks have 27 slots (chest size)
Big backpacks have 54 slots (double chest size)
You can also craft a colored backpack if you put any dye in the middle:
Ender backpack (was Magic backpack before):
Last but not least you can craft an ender backpack (like magic backpack before) which is a portable ender chest which shares its content with the ender chest. You craft it with an ender chest:
You can recolor backpacks by using a dye or the corresponding leather:
You can upgrade any backpack, except the ender backpack, to a big backpack by putting tanned leather around it:
You can make bound leather with two leather in the middle outer slots and strings in all other slots:
You can burn bound leather in a furnance to get tanned leather. One coal is enough for 8 tanned leather.