Get the creative juices flowing among your fellow road trippers by composing a group story. One person in the car starts by creating the first line of the story. You can start with a simple "Once upon a time, there lived a princess" or come up with something more unconventional like, "Joey the frog always had blue spots." Next, each person in the car adds a line, and the story builds and builds. Depending on your group's story telling stamina, you could go on for a few minutes or a few hours.
To make the game more challenging and fun, make a rule that all of the lines rhyme or, instead of going in a circle, call on people to come up with a line. After you've reached your destination, your kids could write and illustrate the story as a token of their road trip adventure.