In regards to stuff to have on hand or bring with you:
- Duct tape to hold stuff still that is moving
- WD-40 to get stuff moving that is not moving
- 12-vdc test light or multimeter
- Mechanics wire to hold stuff still that is moving in places that will get hot where you can't use duct tape
- Wire and wire splices and connectors and tool to work on them
- A Phillips and standard screwdriver in a couple of sizes
- Slip joint, diagonal cutter, and needle nose pliers
- At least two vise grips of different sizes
- At least two adjustable wrenches of different sizes
- 9/16" combination wrench (to use to adjust air brake 'S' cams)
- A hammer for when WD-40 isn't quite enough
This is all in addition to vital fluids, extra fuel filters, and ear plugs (if you are getting an FE you probably will need them for sure).
I also carried a 12-vdc invertor so I could have 110-VAC while on the road. Which required me to wire in a power point where I could plug the invertor in.