I don't know if any of DSC's links mention this, but I'd like to stress an area not related to the car...your physical/mental condition.
1. Eat a big breakfast. I never eat breakfast...except on AutoX days. If it's an afternoon event, eat a big lunch.
2. Get plenty of rest the night before. A tired mind is a slow mind.
3. Take plenty of fluids to drink throughout the day. Things to snack on like potatoe chips and candy bars don't hurt either. At bigger events, I usually take a cooler full of water/poweraid, lunch meat, mustard, a loaf of bread, and snacks. With bigger run groups, after a run you may have time to go fix a sandwich, eat it, and still be ready to go before your next run.
4. Take sunscreen...putting a helmet over burnt ears sucks! (may not apply if you aren't cursed with a Conan O-Brian complection <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/tounge.gif" border="0" valign="absmiddle" alt='

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5. Walk the course as many times as possible. Ideally, it should be stamped in your memory before you even get in your car. Knowing the course like the back of your hand beforehand inspires confidence and, therefore, better performance.
6. Stage early and be ready to go well in advance of your turn to start. If you wait til the last minute to get in your car, put your helmet on, and stage, you'll likely get over-excited from rushing to get ready. Get ready early and slowly and stay calm and collected. While you're in your car with your helmet on waiting your turn, close your eyes and envision the course you have stamped in your memory. Try to envision shift points, braking points, turn-in points, apexes, etc...this will become easier as you get used to your car.