Please don't laugh
I use a diaper bag my wife bought for $20 at JC Penney. She bought one for the kid and when I looked it over I had her buy me one. It has pockets all over, mesh pouches on each end for bottles (milk for the kid, water for me), two main compartments (one with nice little pouches for mags, ammo boxes, etc.), a rubberized zippered diaper pouch (holds hundreds of pieces of brass) and even a cushioned 12"x18" changing pad that works great for gun cleaning, sighting in, etc.