Like you I keep a set of metric and english allen wrenches..just the smaller ones..and a leatherman. Also some of the common star type allen wrenches.
I keep a small straight and phillps head screwdrivers, (a tad bigger than jewelers type..Klein brand..good ones) some of the pistol sight screws are really tiny and easy to bugger.
Quality lens cloth from my Serengeti sunglasses.
Small tube of blue locktite.
Tiny-micro needlenose pliers.
Tiny magnet dish.
Tiny flashlite..(1 aaa battery)
T-handle .22 caliber cleaning rod with 2 extensions. (ram-rod)
Glock front sight wrench
A quarter, dime, and a nickle.
Sharpie.
Heavy duty band aids.
And of course the usual cleaning stuff..tips that fit the .22 rods, patches, oil, clp, rags, silicone cloth, etc.
I can fit all of this in a medium range bag as well as 3 handguns, some ammo, eye and ears, small staple gun, masking tape, spare mags for all my usual's and 2 handgun bench mats.
I leave the phone at the house...no cell service anyway.
This gets me by real well. The secret is keep everything tiny. I'm not gonna be rebuilding a 350 v8 out there ya-know.