Look for a pack that has the thick, soft rubbery stuff along the insides. It will help to keep it from riding down. A wide strap. Water bottle holder(s) are a must. Make sure the bottle holder holds standard water bottles you buy in store. Some come with their own bottles you fill, but I find their tops weird to unscrew.

For pockets, a few various sizes for your specific odds and ends a smaaler comp for cartridges, a medium comp for radio/gps/batteries. And them the large compartment. Look for dividers in large comp so you don't just have a pile of stuff in there with all the small stuff settling to the bottom where you gotta dig for it.

Personally I find "fanny" packs to be rather undersized. I like the larger packs.

Uncle Matt (in IL)