I've found the best cure for this is to travel with two or more dogs to keep each other company. If you can't do this, leaving a radio on and tuned to a talk show station often works. Don't forget that cats get lonely and bored too. Invest in a few catnip toys. Also, since cats are more visually oriented than dogs, they often enjoy watching tv when there is a lot of movement on the screen.
Nature shows can be fascinating to cats.
If your pet requires veterinary care while you're on the road, you don't have to pick a vet at random from the phone book. If your animal companion is of a breed with special health needs, you may want to research on the internet before you travel, to find vets with experience with your breed. If your pet gets lost, try not to panic. First, call your contact person who's phone number is on your pet's collar. If not, call the closest police department and ask if they've had a report of finding a pet like yours.