not sure if this was brought up. if you have a meet and switch, bring your own wrench if you have to readjust the brakes. ( ask shop how, its easy )
i'll probably get backlash on this but I also bring large wrenches to replace or cut and repair airlines, extra lights, extra light cord, de-icer , hammer, for frozen brakes. and assorted other tools for small fixes.
I'd rather repair myself than wait 4 hours for a tow truck.
also blanket, extra water and snacks for breakdowns. also an overnight kit, bathroom kit and spare clothes if you have to layover. it only happened a couple times for me over the years but it was nice to have this stuff in the tractor.
just like anything else you'll learn from experience.