It holds many items. It holds many weapons. It can endure heat, snow, water, the Infected, Hunters, and Fireflies. Despite all it's gone through it sticks with you till the very end both in singleplayer and multiplayer.
I think Joel holds the world record for how fast you can put on a backpack. Seriously... Actually think about how fast he does it. Can u do it that fast? I wish everyone could make a video of them trying to put on a backpack fast. I would watch them all