I have a bunch of mini's
I'm am/was much more fond of the Mini-IIs, that are slightly taller than the standard Mini Systainer, but I haven't seen such in the T-Locs.
Anyway, I use a pair of a more-mobile first aid kit. Bandaids, tweezers, gauze, etc in the upper one, easy to get to. More serious stuff in the lower one. Clipped together it's a little tiny portable clinic (i.e for camping; road trips, etc, and I keep it in my first floor utility closet).
I use a few for holding pistols with up to two extra magazines.
I have the Festool socket set (which is SO nice). Latched to this set, I have another mini which holds a HD "Husky" socket set that was a pretty good fit within the box, and has non-metric sizes.
I use the T-Loc
micro to hold CR2032 and other small batteries for various things-- primarily digital measuring devices, and spare batteries for my ear muffs/ radio.
And I have a red Mini which I used to create a kids toolbox kit for my daughters.
This last one is my favorite use.
