I can only give you recomindations of what I have used mountain climbing. I would go with an internal plastic frame for starts. It will be comfortable and not as bulky. Get a pack with lots of places to attach carabieners so you can hang waterbottles and a camera bag, things like that. I would get a bigger bag made to have a sleeping bag put inside because they are usually water proof on the bottom and even if you don't carry a sleeping bag you can still use the extra storage (in most the extra storage can be pulled up ...

I can only give you recomindations of what I have used mountain climbing. I would go with an internal plastic frame for starts. It will be comfortable and not as bulky. Get a pack with lots of places to attach carabieners so you can hang waterbottles and a camera bag, things like that. I would get a bigger bag made to have a sleeping bag put inside because they are usually water proof on the bottom and even if you don't carry a sleeping bag you can still use the extra storage (in most the extra storage can be pulled up into the bag for a smaller pack). Make sure your pack has shoulder pads that aren't made out of a foam that will break down over time. Make sure it has a stomach strap that is padded and some have places on the strap (sholder or stomach) that you can put a camera or money in for easy reach.With packs expensive is not always better, big 5 has some awsome packs that are cheaper then a lot of REI stuff. Well thats my 2 pennies so message me if you want more info.

Here is one from an old scoutmaster.
http://www.trailflex.com/

I thought this would be an easy answer.because I know what you need. I looked at almost 900 sites and found one that I thought would be close.