My rule of thumb is if it only requires a minor repair but it would keep me from flying, have it in the box. I carry all the hex head wrenches I need to work on my planes, screw drivers, ratchet and sockets, adjustable wrench, needle nose pliers, hemostat, hobby knife, servo screws, wheel collars, control horns, tubing, rubber bands, packing tape, glue, nuts, bolts, washers, glow plugs, fast charger, shrink tubing, a cold solder gun, wire cutters, lengths of cutoff pushrods, zip ties, etc. Whenever I buy parts, I buy extra, then put them in the box. It all fits in a single tool box I purchased from Wal-Mart.

Brad