Exactly what to eat the night before a race depends a lot on you individually, as well as the race distance and your personal goals. Everybody is different, and some people react differently to different foods. (For instance, many can eat peanut butter on a bagel right before a race but protein-rich foods like PB tear my stomach up during the run.)
Then there's "carb loading," which just means filling up on carbohydrate-rich foods to fill your glycogen stores so your body has a readily-available energy source to use as fuel. For some, that looks like pancakes and white rice. For others, a plate of whole wheat or whole grain pasta does the trick. If you can handle a bigger carb load the night before a race, then most find that opting for complex carbs is better (whole grains, whole wheat, etc) because these carbohydrates are broken down slower by the body. However, depending on how far your race distance and how big your serving sizes tend to be, you might be better off doing your carb load two nights before the race and going for something lighter the night before.
Personally, my race strategy is this (no matter the distance): two nights before the race I eat one serving of whole wheat pasta with chicken and vegetables and the night before I have brown rice and grilled salmon. That works well for me, but it might take a couple trial and errors to figure out what is best for you!
For a more in-depth article on nutrition before a race, click here!
Otherwise, make sure you're hydrating! Aim to get 12-16 ounces of fluids in every 2-3 hours the day before a race. Then the morning before a race, try to get another 16-20 ounces. Then make sure you go to the bathroom just before the gun goes off so you're not having to stop to go along the course!
The best piece of advice? Relax! Trust in your training, and if you're feeling apprehensive, remember that race day adrenaline is a very real thing and will get you through the tough parts of the course! Enjoy yourself, and be sure to reward yourself at the end! (Donuts and pizza, anyone?)