These boredom busters are guaranteed to postpone the "are we there yet?" -- at least for a while.
Before you go, make a list of things that you might see along the way: types of animals, buildings, and vehicles, and items that are specific to your route such as a picnic table, a fruit stand, a roadblock, a lighthouse, a lake, or a landmark. As you see each item, check it off your list. You may play the game together or competitively.
Fill a backpack with a child-friendly tape recorder, headphones, and book tapes. Or, pack several backpacks, one for each traveler. Purchase book/tape ensembles, or create your own. Before the trip, have someone read favorite picture books aloud onto a cassette tape. Ring a bell or make some distinctive sound when it's time to turn the page. Pack the books with corresponding tapes and get ready for hours of reading pleasure.
Before your trip, fill a bag with a variety of small items. While traveling, each player reaches into the bag, pulls out an item and includes it in a story. Each player can tell a single story or add a part to a continuous tale. Besides being fun, this activity builds vocabulary skills and creativity. Collect objects during your trip for the homebound story: found objects, small souvenirs, postcards, ticket stubs.