Didn't know you were a Ham Charlie!
First and foremost, a good first aid kit. Bandages, gauze, ace wraps, neosporin, aspirin or tylenol (generic is fine), if you're squeamish about CPR a mouth barrier or something similar, scissors all at a bare minimum.
For tools, generic hand tools in assorted sizes and in both sae and metric (some folks bring odd-ball things like TJs and Infinitys...)
, decently sized hammer or two with cold chisels, punches of assorted sizes, screwdrivers of assorted types and sizes, pry bar. For those of us silly enough to bring TJs, a complete torx set...
Air source if you air down, can be either on-board air or power tank of some sort, if you have a big inverter - some power tools or cordless power tools and extra batteries/charger. Assorted air tools if your air system is stout enough.
If you have welding skills (hopefully I'll develop them soon!) then cables and a few sticks of 7018 as tad mentioned (batteries can/do make adequate "welding machines", as can modified alternators).
I generally have a first aid kit and the hand tools. An air system and welding tools are on the "to do" list...