Obviously, this is an open-ended question. Everybody is different. Some may like trail-mix, while others like potato chips. But here are some good rules-of-thumb:

• Bring along plenty of water and munchies in the car. It will be much cheaper to buy these at the grocery store than pay the convenience store prices. It might also save you some extra stops.
• Sticking to water will be much easier on your body than drinking lots of cola. Remember to avoid large amounts of caffeine. Caffeine can wear on your nerves. If the driver needs large amounts of caffeine to stay awake then it’s time to pull over for the night.
• Have the adults keep control of the munchies so mealtimes aren’t ruined.
• You might want to consider eating a healthy meal or at least bring some healthy snacks
  1. sliced carrots
  2. apple slices
  3. trail mix - nuts, raisins, dried fruits

What you don't want to do is arrive at your destination feeling weighed down and sick. That would take away from your recreation...and what fun would that be?