I carry the usual with me for years, fuses, wire, multimeter valve caps for tires (?) basic tools to tightening or loosening things and a power drill. Recently added a serpentine, oil filter and water separator at the suggestion of Camp Freightliner. During a recent service the old serpentine was found to be split lengthwise. I had them put on the spare and bought a replacement to carry (basic inventory rotation). Note I never intended to do any of the work myself, that was in years past, today MasterCard or Amex if they will take it.