A lot depends on your abilities. I pack a meter to diagnose electrical issues. I also took everything I needed to change any hose or belt. I kept a ScanGauge to diagnose any abnormal codes that might be in memory during an engine malfunction.
I also carried a grease gun so that I could crawl under and grease the chassis on a regular basis as we traveled. Grease is cheaper than parts and I usually never went longer than 1000 miles between greasing the chassis. It also gave me a chance to look underneath the chassis for any problems. I carried several of the extra large white disposable suits used by painters, etc. The are available at Home Depot for a few bucks and they slip on over your regular clothes if you plan on getting dirty. A lot also depends on where you travel. Walmart and their tools are never too far away, as well as hardware and auto parts stores.
