We drive from Minneapolis to Chicago all the time with DS (now 25 months). Key things for us...
#1 - drive at night mostly. We generally start on the drive around 8 - 9 pm, and he sleeps through most of it. I understand, not ideal for all, but DH is a night owl and OK with driving thru the night.
#2 - snacks. A snack trap filled with cereal, or snack size bags with goldfish, minicrackers, snack size sun chips, snack size raisens. The key for us really is the small snack size bag or box, so part of the time is spent by DS just trying to get the food out. Plus he's really happy being able to do it himself.
#3 - toys/books. DS is happy to hold/"read" picture books himself. This may be because he's been exposed to books since he was very small, so may not work for all. Other small toys, esp. ones that sing or make some sounds, can help for a bit.
#4 - songs/counting/games - We will sing over and over things like Itsy Bitsy Spider, Row Row Row your Boat, the ABCs, Twinkle Twinkle, Ring around the Rosy, etc. We will also play our own little "I'm looking game..." where we look and take turns calling out what we see - e.g., Big Truck, Water, Green Tree, etc.
Good luck!