The best pre-race meal is usually familiar, easy to digest, and timed early enough that you are not rushing to the start. A race is not the morning to test a new restaurant, supplement, or giant breakfast.
When to eat
Most runners do well with a normal meal two to four hours before the start, then a small snack closer to the gun if hunger returns. Work backward from your start time and practice the same schedule before long runs.
What to choose
Choose carbohydrate-rich foods you already tolerate: oatmeal, toast, a bagel, rice, a banana, applesauce, or a small serving of cereal. Keep fat, fiber, and large amounts of protein modest if they tend to sit heavily.
How much to drink
Drink normally with breakfast rather than forcing a large volume immediately before the start. Urine color, thirst, weather, and your own long-run experience are more useful than a universal bottle target.