Road trips are always better when you have something to do. So to entertain my mom and I, I purchased Bossypants by Tina Fey on audiobook.
Very possibly one of the best purchases I've ever made. At least for a road trip. I think I would actually recommend this over the book because Tina Fey narrates and you get to hear the book how she meant it.
My mom and I almost had to pull over when we were in Chattanooga because we were laughing so hard. (: