Since I got tired of trying to find a hydration backpack that would work for mtn biking, I decided to take matters into my own hands. I started with a Tamrac Adventure 7 since it has a camera compartment on the bottom and a large compartment on top that could hold a bladder. I started by cutting a hole at the top for the bladder hose and then added a loop to hold the bladder.
I bought the 72 oz Camelbak bladder as it's a little wider and not as tall as the 70 oz bladder and even full it fits fine. I do put the bladder in a plastic bag just in case it leaks. That's also why I use a Camelbak bladder as they have the best reputation for not leaking. I've used them for years and I've never had one leak yet. YMMV.
The camera bag can hold my 50D w/Tamron 17-50, one 430 EXII, 2 PWs or my Sigma 10-20, an angle finder and spare batteries for the camera and flash. I can fit 2 Ultrapods in the mesh pocket in the top. The front zippered pocket holds my wallet, phone and keys.
Since I need to be able to use this pack at places like the North Shore in Vancouver B.C., I added some straps to hold my full face helmet and arm pads for the road climbs.
The helmet straps store nicely in the side mesh pockets when not in use.
It hasn't been crash tested yet, but I'm confident the camera will survive a pretty good one. I had been using a Dakine Nomad with some foam padding and my camera did survive a couple of decent crashes in that. This pack offers even better protection. It's a bit heavy when fully loaded and with a full bladder, but it's doable. The pack itself is only a bit larger than a Camelbak Hawg so it's not too big even for a smaller person like me. I'm 5' 8" and 150 lbs.