I'd say primarily the mat in any given kit needs to be proportional to the depth of tasks that the tools will allow you to undertake; I sometimes feel like safe zones are almost deliberately designed for small parts to get as lost as is possible (they aren't, just feels like it).
I can get on board with something like a multi-tool, tape, maybe allen key set because airsoft guns (especially the ubiquitous AR AEG) are mostly held together with metric allen headed screws and some manufacturers don't tighten stuff up very thoroughly. More than that though and, as said, you really want to be inside a nice, clean, smooth, clutter free room with no gosh darn holes of any kind in the floor.
Some folks will have specific parts on their specific guns where they know they'll need X or Y on a regular basis for whatever reason, but I'd say a medium flat/cross head and 1-5mm allens cover most things on most airsoft replicas. Props to some of the folks in here if you've been doing piston changes on site though and saving the day, that's ballsy lol.