Your diet before a meet or workout should consist primarily of carbohydrates. Energy bars such as PowerBars, Cliff Bars and similar products are very good, as are fruits such as bananas, apples and pears. You may also eat cereal, bagels, or toast. Avoid citrus fruits. Avoid drinking milk (you may have a little on cereal if you choose). Milk produces lactic acid in the body, which is the substance that causes stiffness and pain in your muscles after a hard run. You body will produce enough lactic acid on its own without you having to add to it by drinking a lot of milk.
As you workout, you will find the best combination of things for your body to eat. We had one athlete who did better with more protein, while the general rule is as stated above.