Ziggy - What kind of Camelbak do you have, size and brand? I've never seen them before and I looked them up and that looks like something I'd be interested in getting. Does the little spout work so we could use it to refill our water bottles?
As far as small backpacks go, I've got some from Babe, Shopko and Wal-Mart. The one I currently use is a perfect size. I can carry my money, tickets, sunscreen, camera, video camera and a few other things and it works out great. Check around most larger dept. stores have them, for a pretty good price. I also picked my current one at WDW last year. Some that I have do have the water bottle pocket, some don't.
Pammy