Plinky said, "List your must-haves for a successful road trip."
Assuming you've already got a reliable vehicle, the most important thing is good company – someone who understands that the journey is at least as important as the destination, someone who can happily follow the surprises that come up on a real road trip.
Next is good music. Without that, you are sunk. One of the great things about good company is that you can make your own good music in a pinch, and that's how we used to do it before we had CDs and MP3 players with which to carry many GBs of tunes around.
Next, a cooler filled with drinks. You get thirsty in the car, and its cheaper and more convenient to just take your own water bottles and sodas along. Taking healthy snacks with you is advisable, too. You can skip this step in a pinch, but it's more expensive to travel without them.
Finally, a couple of changes of clothes and your toothbrush. Pack lightly, because you don't go on road trips to look glamorous. You go on them to have fun, period.