Going Traveling, need a camera/storage bag

I'm going to be traveling to Asia this summer to teach English. I want to bring my camera, but right now the only bag I have is the Tamrac Adventure 9. I like the bag, but I plan on only bringing my 30D body and one lens (maybe a 17-55 IS). The Adventure 9 is a little too large on the camera-side of things.

I'm looking for a bag that can hold my 30D and a lens safely and comfortably, but still be able to hold binders, books, a water bottle, and other things in there. I need it to be a backpack, not a shoulder pack because I will be walking miles and miles. I've thought about moving my inserts in my Adventure 9 around a little, but it doesn't look like it will be that good of a solution. That will be my last resort if I can't find a bag I like. Worse come to worse, I'll pick up a G9 and forget finding a photo backpack with a large enough storage area. I've looked at all the Lowepro and Tamrac bags, as well as a few hiking backpacks, but I haven't found a solution that particularly fits my needs.

Anyone have any ideas of a good bag or bag I can easily modify to fit my stuff properly, while still maintaining easy-access to all my gear?

How about a regular backpack for your books & water bottles etc and just cary your camera in a holster or toploader which you can put into your backpack if need be.

Check out the Urban Disguise series at thinktankphoto.com

They look like good bags however they are shoulder bags.

No shoulder bags.
Hmmm I didn't think of putting a smaller camera bag inside my backpack though. I'll think about that one. Any other suggestions would be great!