Originally Posted by albertmoreno

I second the sticky idea.

Tried 2010:
Wingnut Adventure Pack (hydration pack)
I really like this hydration pack because it has plenty of room at 1600 cu. in. for most of my needs as a college student, having a water bladder is much more convenient than using water bottles (at least on longer commutes), and the bicycle-specific features are just awesome and well-thought out. This pack is waterproof, includes compression straps, an emergency whistle on one of the two chest straps, two small mesh pockets that expand to a considerable size, one main mesh pocket on the back where the compression straps are, and two side "wing-pockets" that make it easy to access stuff while still wearing the pack. Also, there is a handy mesh pocket on the front left shoulder strap for cellphones or granola bars. Although, the Adventure Pack is sort of pricey, it has performed excellently. I wouldn't recommend any other backpack/hydration pack. You can get them in various sizes at wingnutgear.com