Have your dog wear its identification all the time. If your dog wanders off and becomes lost, your chances of being reunited are much, much greater if he/she is wearing their tags.
Step2
Make sure your dog is up to date with vaccinations. Nothing could be worse than having your dog contract a disease halfway through the trip that could have been easily prevented. Talk to your veterinarian about vaccinations.
Step3
Never, ever leave your dog in the car alone for any period of time. Dogs can overheat in weather that you would think would be fine. Also, cold temperatures and sitting still can be a health hazard for a dog. Just don't leave them in the car at all. They get lonely anyway.