What altitude?
I do a lot of high-altitude Himalayan hiking (between 10,000ft - 17,000ft) - am actually leaving in a week's time on a project to photograph bears - and my general rule is 1 digicam (currently Panasonic LX-1 or Canon G9) in my pocket while I am walking, and a 40D+17-40+70-200 in my backpack for golden hours shooting. Nothing more. And forget a camera bag. Wrap your kit up in socks, underwater and the sleeping bag, and keep it in your pack. Camera backpacks are the most useless monstrosities for actual extended hiking, given how heavy they are.
The more gear you carry, the more tired you are going to be and the less likely you will want to take photos. So carry as little as possible. You can even get by with a 17-70 style zoom (Galen Rowell did most of his work with a 24mm and a 35-70 Nikkor on his film camera) - often, that is all I carry. In fact, had he been a typical POTNer, he wouldnt even have managed his signature shot, Rainbow over the Potala. The 24-105 would be ideal on a FF camera, but for my tastes, isnt wide enough.
Also, when you are hiking and in your stride, the last thing you will want to do is stop and dig your camera out of a backpack to take shots, for that matter. And carrying a DSLR in the ready is an exercise in frustration as it flops and bangs around. So carry a compact.
Lastly - lose the flash.
Vandit