I used to try to keep everything I needed in my field box, but it ended up over 40 lbs!!! I took all the tools and most parts and put them in a small tool box. In the flight box I store props, glow plugs, some control horns, rubber bands, electric starter, electric glow driver, battery glow driver, and a manual pump for the fuel. I highly recommend the manual pump and the battery driver in case your power panel or box battery goes bad.
Field tools include an adjustable wrench, vise grips, channel locks, regular pliers, needle nose pliers, long shaft screw drivers, packing tape, electrical tape, allen wrenches (metric and standard), wire ties, and some spare foam. Hope this helps you out. (there is a good thread here on rcu about field boxes if you do a search) Good Luck Loren