Squeak or croak your way for entertainment. Make up a "Where Do You Hear It?" game to provoke a lot of laughter among your travelers. Hilarity will ensue when people think up everyday sounds to mimic, like that of a toilet flushing or a toaster popping up. As this game evolves, you don't have to be limited by household items either. Change the game up so that participants try to make noises like animals or acts of nature as well.
Use the music played in your car to create your own "Name the Tune" game. If you feel everyone becoming restless, have a passenger use the volume control to allow just a few seconds of a song to play and then ask fellow travelers to guess what song they just heard. Switch it up so that the music coordinates with your destination too, such as tropical music if you're headed to the beach. Keep track of correct answers and make up a prize: for example, when someone reaches a score of 20, the winner may have control over the radio for the next hour or so.
Make up a game that is more about where you are going and educational as well. If you're on a long road trip, as you pass through larger metropolitan areas along the way, have everyone write down or name out loud ten things they can think of about that city. For example, if you drive through Indianapolis, a player could list, "Super Bowl Champions" and "Indianapolis 500." By the time everyone gets through their lists, you'll be on to your next city.
Create a game with the little ones to pass time while traveling by car. Ask them how high they would like to count. Encourage them to stay under the number 20 or so. Have the kids count the cars coming at you from the opposite direction until they reach that number. When you reach that car, use the color of the car as reference and then have the kids say something they want to do when you reach your destination that starts with the same letter. For example if the tenth car is a silver, the child could say "swimming." Time will pass quickly as you all think about the fun things you want to do when you arrive.