Backpack

Backpacks are unlocked in the Leather collection, and can be interacted with to open and store items. It can be opened by right clicking while in the main hand or by right clicking on it when it is in any slot of the inventory, ender chest, etc. Backpacks can also be dyed to any color.

Crafting
There are 5 sizes of the backpack:

Dyeing
Backpacks can be colored with 8 of any color Dye. (Backpack in middle surrounded by a single color of Dye)

Example (using Gray Dye):

An overview of all colored backpacks:

Trivia

 * A backpack cannot be placed in another backpack, nor sold to an NPC.
 * Backpacks are notorious items used in Scams by hiding junk items inside and trading them away as something else. A hidden update on May 27, 2020 revealed that item names were stored inside a backpack, making backpack scams less effective; this change has since been reverted.