1. Don't stay up until well after midnight on the eve of departure because you can't really sleep for long with three young children in the car.
2. Check out this site for some great activities and ideas to keep young kids amused during long car trips (thanks for the tip Lou) & this if you need some extra ammo in your arsinal. It actually helped make it a surprisingly pleasant trip - despite my quite serious fears otherwise.
3. On your way home, after an exhausting week at the beach in the rain with 14 people in the one house and little sleep, do not under any circumstances drive your car out onto the edge of a salt lake, even if that salt lake is pink. Your trip home may take longer than the short 9 hours originally anticipated. After more than a few hours I found my self wishing for whinging kids in the back seat of a moving car.