My field box is minimally sized to hold a 12 volt battery and a 50 ounce detergent bottle for fuel. I carry a starter, a pump and a kwick klip. For tools, I carry a 4 in one screw driver, a prop reamer and a four way wrench. I add a jewlers screwdriver that fits the low end needle on my OS engines. I also carry a 5/64 and 3/32 ball driver because I use socket head screws for most everything.

For spare parts I have a small (1x3x5) Plano fly box. I velcroed it to the side of the flight box. It holds one of every fastener used on the plane, a couple of spare clevises and wheel collars, a couple of spare glow plugs, and a selection of allen wrenches for the little set screws on wheel collars of all sizes. I carry a couple of spare prop nuts, a bit of extra fuel line and a small bottle of CA. I tuck a spare prop or two in next to the fuel bottle. The whole thing weighs under eight pounds.