Wow - interesting thread. I have taken more than a few road trips to pick up stuff and despite a lot of preparation almost never had a trip go by without some problems. That's the main reason my wife won't take any more trips with me. With so many items being purchased by GL etc and moved by the buyer I thought some safety comments were in order. Here are some rules that have kept me mostly out of trouble.
1: Do the research and read the TM. If you know what you are driving or hauling you are less likely to get into a problem you can't fix.
2: Read the posts of others on the site about potential problems with your vehicle.
3: Know your route and have emergency back-up plans along the route.
4: Bring some basic tools (screw drivers, wrenches, flashlight)
5: Bring some basic parts - filters, fluids, belts, 5 gal gas can, air line, duct tape, extra fuses and light bulbs etc..
6: Bring appropriate clothes, gloves, carharts etc.. in case you have to walk a distance or get under the vehicle.
7: Emergency flares,
8: Charged cell phone
9: Have someone at home that can coordinate help if you get stuck
10: First aid kit with some energy bars
11: If you can't get the vehicle inspected by a pro - do it yourself. Make sure the lights and blinkers work, tires are good and hold air, fluids topped off, no leaks, brakes working... Once you get behind the wheel you are responsible for the condition of your vehicle. A unsafe vehicle is not only unsafe for the driver, but for others on the road.
12: Finally, expect everything to go wrong - it usually will, but with some basic prep yu can keep yourself and others from getting injured.
I am sure I am missing some important things these are my thoughts FWIW.