I had a similar brain flash onetime, when I was carrying two tool boxes in to peoples houses to install deadbolts. The only thing I took out of the one box was two 2 1/8 bits, so I put them in the other box. Makes things lighter.
I do have a very old cardboard box from a Von Duprin closer, which I use for steering wheel tools. Oughta get a different box sometime, it's held together with duct tape at the moment.
I have a Sterlite box (shoebox size) with a couple fishing tackle lure boxes (y'know, about4 x 6 inches clear plastic with sections about an inch square) for tumblers. In there also my followers, tweezers, and so on. Key gage. Small file. That sure comes in handy. I've got Kwikset and Schlage bottom pins. Sometimes in miserable weather I can take the "other car" and just grab the rekeying box.
How about on your .50 cal box, get some fuzzy self adhesive feet, so you aren't scratching customers floors?