Depends on how far I'm going and what else I'm carrying.
If I don't need to take other (non-camera) stuff with me, I'll use a Mountainsmith Tour Lumbar Pack. It can accommodate my 6x7 body/back/prism/lens, plus an extra back, small light meter, and a couple of extra lenses if I want. It also works nice for my digital Rebel & lenses.
For longer day-hikes, I use 44-liter daypack. It has full zipper front panel (as opposed to top-loading), and 2 full-length zipper pouches on the sides that I can reach into without taking the pack off. I can fit 2 lenses in each side (or teleconverters, or extension tubes, or filter pouches.) SLR+lens hung from the shoulder straps using Tamrac "Backpack Camera Straps" (N-11). Detaches with a quick-release buckle for taking the pack off or shooting using Live View. If I hook one of the 2 sides under the chest strap of the pack, it tends to keep it from bouncing against your chest (or gut) as you walk. Camera is "wrapped" in a Zing neoprene "camera condom" (as my wife likes to call it). All the camera gear, plus a tripod (Gitzo 1126 or a cheap carbon-fiber), water bladder, food, first-aid and the rest of the "10 essentials" fits pretty well.
For overnight/multi-day. I still hang the SLR+lens from the shoulder straps of my backpack. Lighter weight lenses (like the 70-300 IS as opposed to the 70-200 f/2.8 L, and 24-85 instead of 24-70 L) go in padded pouches that hang from the waist-belt of the pack. Tripod still gets strapped to the side of the pack.
You asked...so there's your answer
--Greg