Don't let the thrill of the trip keep you from making sure your car is in tip-top condition. Have your oil checked, your tires inspected and filled with air, and test the air conditioning and wiper blades to make sure they're working correctly. Have your driver's license, insurance card and contact numbers for roadside assistance readily accessible.
If you don't know how to change a flat tire, learn how to do so before you take to the highways. Ensure that your spare tire is in good shape, and that the jack and other essential tools are easy to access. Your emergency toolkit should also include an orange flag or pylon that you can use to signal for help if needed.
Another word to the wise: Take along a spare set of keys in case they get locked inside the car or dropped from your pocket at a county fair. Give a set to your travel buddy or pack a set in your luggage for safekeeping -- even if you have to call locksmith to open the car, you'll be able to drive when it's unlocked.