When the kids say they're hungry or thirsty, it's often code for "I'm bored." Be prepared with a collapsible cooler of healthy treats. That'll prevent you from making a pit stop for high-priced, salty or sugary snacks.
Bite size pieces of fruit, snack size bags of pretzels, animal crackers, and trail mix are nutritious and manageable choices. Choose bottled water and juice bags with straws for quenching thirst and reducing the chance of spills or dribbles. If you freeze the drinks in advance, they can help keep other beverages and food in the cooler chilly, and a melting drink takes longer to consume.
To avoid the question of where to stop and eat along the road, pack a picnic lunch. A meal prepared at home will be made just the way each person likes it, and a picnic spot, especially one with a playground, allows everyone to stretch and burn off steam before getting back on the road.