I use the Lowepro Flipside 450, but it is more of a daysack than a proper hiking/camping bag. It splits the body into two compartments, the lower with back access for camera gear and the upper compartment for general purpose stuff, although the divider is not sealed and can be removed, if desired, to make the bag more like a conventional rucksack. I usually carry a small pop-up umbrella, snacks, a lightweight waterproof jacket, spare batteries, cleaning cloth and a 1m diameter folding reflector (for natural reflected sidelighting or as a shade while doing macro).
It has a front zipped area that can house a pad or small laptop that could easily hold a hydration bag of some sort, but I bring along my camera manual for light reading!! I usually carry a water bottle or flask in one of the side mesh pockets and a travel tripod in the other side.
I wouldn't like to use it for extended camping out, though
On a recent trip abroad I used it as my walk-on flight luggage. Having taken out the photography gear I didn't need to carry with me on the trip I used the empty spaces in the camera compartment to take spare underwear, socks, t-shirt and wash kit with me. It was all very organised!!