My junk drawer is actually a pull out drawer under one of the dinette seats that I added dividers to. It's not really a "junk" drawer. Everything in it has a use or potential use, tool collection with screwdrivers, pliers, socket set, torque wrench, wire strippers and connectors, plumbing fittings, spare propane regulator, coax strippers and connectors, fudrs, circuit breakers, volt-ohm meter, a few specialty tools, and just about anything that if needed would ruin a camping trip if I didn't have it. If I need to buy a part to do a repair, I buy two, one to use immediately and the other in case it happens again. It is constantly evolving. items are being added as needed and those not being used are taken out to reduce clutter. I don't think there is a comprehensive 'must have" list anywhere because everyone's needs are going to vary. Consider electrical and mechanical ability also. It does no good to have a tool if you don't know how to use it to fix a problem.
The diamond tread storage box on the rear is a different animal. Air compressor, hose, and air chuck, spare power cord, screw jacks, X-chocks, adapters for all of the power configurations
