Check your spare tire for pressure, and keep a tire plug kit in your glove box, right next to your gun
Make sure your lug wrench and jack are available/working.
$300 cash in 20's, flashlight, cell phone, spare set of headlight bulbs and tail light bulbs, small tool kit with all the necessary tools, wet wipes, paper towels, tissues, diapers (oh wait, nevermind), jumper cables, etc. Check the torque on your lug nuts just before leaving, and tire pressure of course. Crawl up underneath it and spot check bolts, nuts, etc, mainly anything doing doing with your suspension.
Oh, and if you aren't armed on a road trip, you are insane, especially if you are planning on doing any night driving. I have a couple experiences in mind, that I'm glad I was armed (nothing happened, but shit coulda got ugly).