I carry a 4-way lug wrench that has stayed with me through 4 different RV trailers and two sailboat trailers. I like the 4-way wrench because it is easy to get plenty of torque to remove a stubborn lug nut without the danger of butchering the nut with a typical lug wrench that tends to twist crooked.
As for other tools, I carry one of the tool assortments that is fitted into a plastic case with both English and metric sizes. The kit rides nicely on the hump under the back seat of my truck. The tools are not real high quality, but for emergency use they are plenty satisfactory. My wife bought me the kit at Pep Boys as a birthday present. Sears has some very nice similar kits.
I also carry a 12v
compressor, a tire gage, a box of throwaway gloves, and a plastic box that has a crimping tool, longnose pliers, test light, electrical tape, and an assortment of wire splices and wire taps.