I have an old sturdy plastic milk crate that is my "Go" box for XC. I keep it packed and stocked so I can just throw it in the baggage area. It has a set of basic hand tools, chocks, tie down ropes, and a plastic compartment organizer with a selection of common hardware such as cotter pins, lock nuts, butt splices, fuses, bulbs, etc. For tools, a 1/4" socket set, box end wrench set, assorted screwdrivers and pliers, multimeter, stripper/crimper, and utility knife will cover many situations. If you do a lot of grass strips, add stakes and a hammer. Oh, and spare usb cables.
I had a problem on a trip once and bought cheap tools from Autozone, only to have the pliers literally break in my hand. After that trip, I bought decent Craftsman stuff.
Safety wire and duct tape are surprisingly versatile. For example, enroute to Oshkosh I noticed an unusual draft hitting my face in the cabin. I investigated and found that a hinge pin on my side window had failed. This was on a Saturday evening at a state park airstrip in rural Kentucky, so a credit card wasn't much help. A couple of loops of safety wire allowed me to continue my trip without delay.