Chances are, if you're a good pet owner, then your dog or cat has plenty of toys at home to keep it occupied. You need to bring as many of these along as you can without comprising the genius of your packing skills. A good chew toy can keep a dog occupied for hours at a time. Many chew toys come with hollowed out centers. Stuff some treats inside it and watch as your lovable mutt spends the next two hours trying to get to the good stuff.
Besides their favorite toys, buy some new ones to keep them interested. Larger dogs can make good work out of a nylon bone. Cats are little trickier. If you have a riding partner or the whole family on board, encourage them to play with the cat on the road. A cat can also spend some time outside the crate if you have others in the car to keep up with it. Just don't try to do these things if you're the lone human in the car. It's too easy to get distracted by trying to play with your pet while you're driving. And while you want your pet to be entertained, you also want to get to your destination safely.