I've heard this so far:
1.) Eat a substantial breakfast, but not too heavy, approximately 2-3 hours before your test time. You should feel full, but not overly full to the point of feeling lethargic/sleepy.
2.) Eat healthy foods, such as fruits, oatmeal, bananas, wheat bagels, etc. and avoid overly fatty or sugary foods (e.g., french fries, hot dogs, candy, etc.).
3.) Don't deviate from your routine when it comes to caffeine (assuming your routine is a reasonable one). If you normally drink coffee, then sure have some if you like. If you do not, then don't all of a sudden on test day drink coffee or a Red Bull, etc. thinking that it will enhance your concentration and performance (it might, but you may not know how you'd react).
The caveat here was that your normal caffeine amt. was "normal" (meaning healthy and non-intefering w/ mental capacity).

4.) Snacking is OK during LSAT breaks, but make sure they are light snacks and not meals. For example, a single banana or granola bar. But not a full meal. And, again, healthy is desired. No chips or soda, etc.
What other tips have you guys heard. What were your own experiences? What worked and what didn't? Feel free to critique my list above as well. Let the advice begin....
