As promised, some photos of the innards that some reviews didn't cover.
Outlet for any hydration reservoir.
A top pocket for small stuff, able to fit your passport and other random stuff. Soft interior.
The insides! That huge bag in the middle is for the hydration reservoir. There is still tons of space even after stuffing a 2.5L one in. (MSR ones only)
One of the sides with things. A zippered pocket for your less important things, or things you don't access to often.
Easy access pouch for putting your map, or a foldable cap when you don't need to carry it.