I haven't used this extensively yet, but I took it out a test hike last weekend with the family. While you'd never confuse this with a full-size backpack, it has a lot of room. The main pocket has a zipper that allows the pocket to expand. There's a small pocket at the top for an MP3 player, and a mid-sized pocket on the back. Plenty of room for a lunch, sunscreen, and a lightweight jacket. At 2 liters, there's plenty to drink. A particularly nice touch is that most of the straps have velcro wraps to keep them from dragging on the ground or getting caught in something. The one downside I've found is that the top chest strap is fully extended on my non-bodybuilder chest and feels a little constricting. I checked it against my boys' MiniMules (a Camelbak for kids), and the length of their chest strap was the same as mine. Overall, an excellent product.