Whatever suits you best. The less you carry, the better - so pick your field box accordingly. For my two .32, 48" sport planes. I carry a fueler box (fuel container and crank pump) that also halds spare props and plugs, plug lighter a plug and prop wrench, and a chicken stick. This is what I carry to the flight line/starting area. It's about 8" x 8" x 15 and holds a half gallon of fuel. It weighs about 6 pounds. I also carry a tool/spare parts box. It's a 3" x 6" x 15" plastic tool box I got at Big Lots for about $3. Think what you need to carry to make MINOR repairs/replacements at the field. I carry one of every screw and fitting my planes use, servo arm, hinge, wheel collar, prop nut, fuel line, 100 mph tape, and a couple other things. I also carry the tools needed to replace or repair these items. Any more than a minor repair needs to be taken back the the shop and repaired properly. This box weighs 3 pounds. Naturally, if your engine won't hand start, you must carry a battery and starter, so your boxes will be larger.

Dr.1