^^^^ many great ideas above.
I carry two spare tires, ever try to find another, when you are 500 miles from a sizable town, on a Sunday?
Also carry a spare vent cover, lost one in rainy Oregon, had to MacGyver a wood and tarp cover in the rain, with a borrowed ladder. Now carry a collapsible ladder as well.
Teflon spray, for door latches, trailer screw jacks.
Square drive screw bits, Gorilla tape, liquid nails, tube of polyurethane caulk.
2x4 short pieces, for more leveling.
Big bottle jack. Coffee can of screws, bolts nuts, washers, old RV hardware
I'm sure there's more!