1. Keep your pets safe and secure in a well-ventilated crate or carrier. There are a variety of wire mesh, hard plastic and soft-sided carriers available. Whatever you choose, make sure it’s large enough for your pet to stand, sit, lie down and turn around in. And P.S., it’s smart to get your pet used to the carrier in the comfort of your home before your trip.
2. Get your pet geared up for a long trip by taking him on a series of short drives first, gradually lengthening time spent in the car. And please be sure to always secure the crate so it won’t slide or shift in the event of a quick stop.
3. Your pet’s travel-feeding schedule should start with a light meal three to four hours prior to departure. Don’t feed your furry friend in a moving vehicle—even if it is a long drive.
4. Never leave your animal alone in a parked vehicle. On a hot day, even with the windows open, a parked automobile can become a furnace in no time, and heatstroke can develop. In cold weather, a car can act as a refrigerator, holding in the cold and causing the animal to freeze to death.
5. What in your pet’s traveling kit? In addition to travel papers, food, bowl, leash, a waste scoop, plastic bags, grooming supplies, medication and a pet first-aid kit, pack a favorite toy or pillow to give your pet a sense of familiarity.
6. Make sure your pet has a microchip for identification and wears a collar with a tag imprinted with your home address, as well as a temporary travel tag with your cell phone, destination phone number and any other relevant contact information. Canines should wear flat (never choke!) collars, please.
7. Don’t allow your pet to ride with his head outside the window. He could be injured by flying objects. And please keep him in the back seat in his crate or with a harness attached to a seat buckle.
8. Traveling across state lines? Bring along your pet’s rabies vaccination record, as some states requires this proof at certain interstate crossings. While this generally isn’t a problem, it’s always smart to be on the safe side.
9. When it comes to H2O, we say BYO. Opt for bottled water or tap water stored in plastic jugs. Drinking water from an area he’s not used to could result in tummy upset for your pet.
10. If you travel frequently with your pet, you may want to invest in rubberized floor liners and waterproof seat covers, available at auto product retailers.

From: http://www.aspca.org/pet-care/car-travel-tips