Cows in the Graveyard: Driving through farm country? In this game, each person or team picks one side of the road, and counts all the cows they see (if you see a herd that's too large to count quickly, just call it 20). Each team keeps a running total of their cows and after a certain amount of time, or when you reach a certain landmark, whoever has the most cows wins. You can also decide the winner by a certain number of cows; for instance, whoever reaches 200 cows first wins. But here's the catch: If there's a graveyard or cemetery on your side of the road, you "bury" all of your cows, and have to start counting all over again!
State Plates: Try to spot as many difference state or province license plates as you can. The first person to see a particular plate gets to count it. Whoever spots the most states and provinces in a certain time or distance wins, or you can work together to try to get as many as possible.
Alpha-Plates: Try to find every letter of the alphabet on license plates, IN ORDER. The game starts when you see the first A, and then you have to wait until you see a B (on a different plate), and so on. Play against ach other or work together to see how fast you can get to Z. If you want to make it easier, you can also play this game with billboards, road signs, or words written on trucks or bumper stickers.
Color Bugs: Pick a particular style or make of car (VW Beetles work well because they're easy to spot, but you could also pick vans, convertibles, etc), and see who can find the car in the most colors.
I'm Going on a Road Trip: Each player goes in turn, picking items to pack for an imaginary trip and listing them alphabetically. The first person must choose something starting with A, as in "I'm going on a road trip, and I'm taking an aardvark." Now the next person gets to choose something beginning with a B, but must first state what has already been chosen, as in "I'm going on a road trip, and I'm taking an aardvark and a basketball." The game goes from person to person, with each player having to say the entire list that has come before-all the way to Z. This can be a tricky and fun memory game, especially if you make some way-out packing choices!
Scavenger Hunt: Before you hit the road, have an adult help you make a long list of things you might see on your journey. These might include a grain silo, a billboard for a particular product, a white church, a corral of horses, a green minivan, a hill with a single tree on it-and so forth. Keep the lists with you in the car, and see who can check off the most items. The first person to spot an item on the list gets to claim it, and the other must wait until they see the same thing somewhere down the road.