When traveling with pets, bringing along the family pet makes for a better vacation for everyone. After the kids are packed, pack a bag for your cats and dogs, especially on a road trip. It will make everyone more comfortable and save time driving around looking for a store that carries exactly what you need while you're on the road.

For Dogs:
Treats - These are used for rewards of good behavior, bribes and just plain fun.
Pooper scooper and clean-up bags - Many cities and towns have ordinances. Even if they don't, be a courteous visitor.
Sweaters - Bring a sweater for cold outdoor weather outdoors. If your dog or cat has sensitive paws, consider booties for outings. Watch for shivering fur in the car or hotels. Make a light blanket available when all of the windows are open.
Toys - Pack something to chew on, something to run with and people-interactive toys. It's vacation. It's supposed to be fun.

For Cats:
Litter Box - The litter box is probably the most important part of traveling with your cats. Designate a private litter box area and show your feline where it is. Don't put it next to the food.
Toys - Bring your cat's favorite ball and stuffed mouse. A stick with a string is a good way to stay occupied in a hotel room while you're all watching TV.
Collar - Make sure your cat has ID and a collar. Cats without collars are often mistaken for runaways. If you become separated, a collar and ownership tag could keep your kitty out of jail in a strange city.

For Both:
A leash and a harness or collar - They don't need to ride on a leash, but it should be at the ready.
Water - Bring a jug of cold water filled up from your faucet at home. Water from a hotel's faucet may taste the same to you, but to them it might taste or smell funny. Keep them hydrated, especially if they're stressed.
Regular brand food - Bring enough for regular feedings and 2 or 3 extras, just in case.
Bed - Bring something to lie on in the car and in hotels. Whether it's a soft blanket, favorite bedding or a travel crate, make it cozy.
Paperwork - Bring the name, phone number and address of your vet. Make sure their rabies vaccines are up-to-date and make a copy of it to bring on the road with you.