The Green Backpack can be found in Cabin 1. In it you'll find Matches, Sunglasses and a Bong. You can also add items into the backpack and the storage seems to be infinite, but only for certain types of items.
The Backpack can hold: Beer, Bong, Dirty Underwear, Hammer, Kitchen Knife, Matches, Paintbrush, Saucepan, Sock. Most large things like the Axe, the Rake, and boxes can't be put into the backpack.