I use a Kelty (www.kelty.com) multi-day internal frame pack for my bug out bag (BOB). It holds 2800 cubic inches, has a 2 liter hydration pack, and has an exterior shovel pocket and loop that can hold an ax, walking stick, or my rifle--although I don't ever use it for that because it bumps me on the bum when I walk shocked

It has some mesh pockets on the side that I stick my ditch kit in.

I adore it.