A wagon? Are you nuts? This simply will not do. You're limiting yourself considerably with the confined space of a wagon. You need to upgrade immediately to something that will allow you to nail up a 8' wide by 3' tall pegboard on each side of a small trailer, carry all of Dubro and Sullivan hardware, with at least two 50' spools of fuel line in different diameters, and bring at least one JR radio, one Futaba radio, and possibly one of each in 72Mhz and 2.4Ghz. You need all the crystals from 11-60 in Futaba, Hitec, JR, and Multiplex or you're just completely unprepared here. Don't stop there, you need spare switches, different thicknesses of CA, extra servo hardware for Hitec, Futaba, JR, and that goes for standard and mini, micro and submicro. Don't forget to hinge a work area so you can do emergency repairs no matter how large.
You completely are shooting yourself in the foot if you don't have everything for gassers too. I think you should possibly get a golf cart with a trailer behind it. An aluminum frame on top to shade you from the sun wouldn't be going to far here. Do not be short sighted, have a cabinet with everything a fire department would have on hand for first aid. Model Aviation magazine just did a Jet article practically cover to cover, so get a fire extinguisher and have a compartment for all AMA forms on hand.
Organize the APC props, pylon props, E props, in all available pitches from 5" up to 23". It would be a sin to not have everything on hand, avoiding ending a flying day due to leaving something behind at a hobby shop. You need at least three 12v batteries on board with chargers for every battery made for the hobby.

The good news is you can donate the tiny wagon to a child in need.