My older sister used a Duluth Pack shell bag for a book bag in college. I have used it for back country fishing. It now serves as a map/book case more than anything else. It has a divider inside and I have tossed a compass, extra rounds, a knife, etc. in there.
A former employer issued us a similar model made by Jacquart Fabric, the Stormy Kromer people. We carried our water, snacks, map in one section and extra cans of tree marking paint in the other so we didn't have to return to the truck so often.