here's what I use for my flight line box http://www2.towerhobbies.com/cgi-bin...?&I=LXJC65&P=7 it holds a small battery,power pannel,glow igniter,a couple of screw drivers,extra glow plugs,some small stuff and my elec.starter.
and its cheap.
then I have the extra gear in a regular tool box in the truck.

if somthing is broken to the point I can't fly it, then I will usually go to plan B and get the other plane out that I brought and fly that.
when I have fixed stuff at the field that was somewhat major, I always seem to have to re-fix it any way in the shop.
so now I would rather take my time and not miss anything, that I could have missed at the field because I had to get "that" plane in the air.
it pays to have a back up plan.