Fortunately, I had bought a CamelBak Classic at REI on sale for $25 or so, when I thought I wanted something small and light, with the minimal carrying capacity it would offer. Ends up, I was wrong.
The Endurance pack rocks in that I can throw in a light shell, or other various clothing, and has plenty of pockets for electronic gadgets, wallet, keys, etc. This is my first bag with a true suspension system, and running with a hydration pack, and not having it jostle excessively is great.