Audiobooks. You WILL get tired of listening to music at some point. Music also tends to put me to sleep. Listening to a book keeps you engaged, entertained, and awake. Crime novels or thrillers are the way to go.
Be careful how low you let your tank get, especially in middle-of-nowhere Wyoming. My buddies and I nearly ran out of gas out there around 3AM. We found a station, but it wasn't open. Had to just sit there till they finally did. Not too fun.
Bring toilet paper. There will likely be a time when you need to shit and there are no bathrooms around (like in the above running out of gas situation). Wiping with paper is way better than leaves or some shit.
Are you doing it alone? If so, be sure not to push yourself too far without sleep. Driving all day is actually really really draining because you have to be focused and on your game 100% of the time.
When I drove out west with 3 buddies, we each drove for a tank of gas at a time and rotated through drivers. That ended up being about 6-7 hours of driving each at a time. After you drive, you are the co-pilot for the driver. The 2 people in the back sleep. If you are driving through the night it is extremely important that those 2 actually sleep. Otherwise you won't make it through the night.
Sounds cliche, but take a lot of pictures. You will regret it you don't.