My box has:
Vice grips
10" Crescent
screwdrivers, Square phillips torx
needle nose pliers
slip jaw pliers
1/2" breaker bar with thick wall socket for lugs
cheater bar.
I also keep
zip ties
extra pins and clips for the hitch
electrical tape
duct tape
For longer trips out of the local area I carry a small compressor and an electric impact wrench
Mission creep is hard to avoid, I try to keep it to a bare minimum.
If you do have a problem on site, make a showy display of your problem. There will be some guy in camp that carries an entire machine shop with him, and he will be more than happy to get some use out of the 300# of tools he lugs around every day.