I spy is another kids' classic. Players take turns spotting an object and the others try to guess what they've got their eye on.
There are a number of ways to play this game, but here's a short rundown of the basics. The thing spied can be inside the car, outside the car or either. If outside the car, the person who's picked might need to inform the other players if the object has gone out of sight.
Usually there's a hint -- the person might tell the other passengers what's the color of the thing they've chosen, for example, or perhaps the shape or the first letter of its name. ("I spy something green" or "I spy something that starts with the letter A".) The questioners then typically look around for potential objects and take turns querying whether they too have spied correctly.