Plenty of road trippers try to drive from gas stop to gas stop, and this is the only time they get out of the car and walk around; they do this because they assume this speeds the trip along, but you should actually plan to stop at least once every two hours so you can get out and walk around, as this will keep you awake - which is far more important!
Also, you ought to consider stopping for short naps whenever you get tired, instead of just loading up on more caffeine; you can usually nap safely at rest stops during the day, and you can nap safely at most well-lit travel stops at any time of day or night.
And one thing many people fail to pay attention to is the prudence of slowing down their speed at nighttime; when you are on a long road trip, the last thing you want to do is hit a deer or another animal and injure your car and yourself - so slow down at night, and keep your eyes peeled!
When you are going to be driving long distances, keep your eyes open for things you can do to keep yourself awake and alert, and as you uncover the things that work for you, keep these three things in mind as well!