I have been running a Eberlestock half track for the past 2 seasons. They are around 32L with lots of molle to attach stuff to on the outside. What I look for in a pack is a full front opening zipper so I can lay my pack down and get to everything. this way I dont have to worry about taking everything out to get to the last piece of kit at the bottom. in my pack I usually carry a bullet binder with 120 rounds, solo sac, rear bag, rain jacket, food, sling, and a drop pouch I keep all my stage stuff in like COF, kestrel, pen, etc. in the top pouch is phone, keys, ear buds, etc. In side pouches are repair tools, rain cover for rifle, water, and tripod. All loaded up it is pushing 30lb. I find the bigger pack you have the more crap you carry. 32L class packs are a good balance. Try not to cheap out on a pack you definetly get what you pay for. I drug a deer out of the bush with this pack and a rope tied to the bottom molle a couple years ago with no issue.
cheers
Ryan