The longest road trip we've taken with our children was 12 hours and leaving earlier in the morning creates a more peaceful experience. The kids are still sleepy and sleep the majority of the trip. When we arrive to our destination the kids are excited and ready to play.
I pack lots of snacks for the kids. Mostly healthy snacks, including fruit but I also add a few treats that they normally don't get to enjoy. I save them for when we're closer to our destination as a surprise treat.
During long road trips, we always pack their favorite toys. When we're traveling longer distances, I purchase a new toy and give it to them during the trip. This keeps them entertained because they're so excited to have something new.
Be sure to pack a first aid kit, medicine, napkins, baby wipes, cleansing wipes, sanitizer, water, blankets, paper bags for soiled clothes, change of clothes, and extra food. These items should be packed separately and within close reach.