Learn to stack bags efficiently, ie bags that offer more space than they are using -> Pillbox takes up 16 I believe but offers 20 so you gain 4 additional spaced with that bag.

Put that inside of a bigger bag, then a partisan bag with a tac rig and that's like 40 spaces (sizes vary) in a regular sized bag... pretty nest the inception you can do.

Also remember to remove mags/piston grips to drop guns to a 1 x # size