Bring lots and lots of snacks, treats and amusements.

Car games like “I spy” are a time-honored tradition.

Allow time to stop at restaurants or local playgrounds so the kids can run around.  Bring a ball or Frisbee, too.

Try to stop at restaurants with play areas.  Let the kids work off some energy—maybe even let them eat their meals later, in the car.

Alternatively, create picnic meals (depending on the weather) with food bought from restaurants or the deli—this saves money, and gives the kids a chance to play outside.

Change the kids’ seating arrangements to minimize conflicts.

Give maps to the older kids,     and let them mark off your route and navigate.

Allow sleeping children plenty of wake-up time:  start the wake-up process long before you’re going to stop the car.

Brining along a potty can be a great idea if your children are very young.

Depending on your family policy on TV/media consumption, you might want to look into renting VCR/TV units for your vehicles.  Or bring along a DVD if your laptop plays them:  a fairly inexpensive gadget lets you plug into your car’s energy supply.

Special car-travel kits can be a good idea:  for ex., a travel desk suspended from the front seat of a van is perfect for a child to draw, store crayons, etc.

With small kids, over-preparing is always better then under-preparing.