First, let me start off by saying that everyone is different, so what works for one person may not work for another when it comes to fueling your body before and during a race. The most general and sound advice I can give you is to get enough sleep and water over the next few days. Good advice any day but with a Sunday race, Friday is probably the most important day to be strict about this.
If you respond well to carbs be sure to have small meals of pasta, rice, bread, oatmeal, bananas, etc. now through Friday evening. No need to overdo it, just until you are full should suffice.
If carbs are not for you, check out this website – Gluten Free Athlete for nutrition advice.
For race day consider eating something light about 2-3 hours before your start time, oatmeal, banana, yogurt, bagel or toast with a little almond butter, hard boiled egg, smoothie, an energy bar, etc. You want your body to be able to digest your meal before the race start, so the 2-3 hours is a general rule. Eat what you are comfortable with, race day is not the time to try something new.
During the race fuel with adequate amounts of water (mostly during the bike but try not to overdo it so you are not too full on the run; there will be 2 water stations on the run as well) and maybe an energy bar or energy gel on the bike around mile 11 or 12. Coconut water or another natural electrolyte drink (no Gatorade please) can be used as well but are probably not necessary since we will be racing for 2 hours or less.
Post race nutrition should be in the form of a protein/carb combo. Chocolate milk is good and I’m sure snacks will be provided by the Xxtra Mile, like bananas, etc.
We are fortunate in the fact that a sprint distance triathlon will not take us too long to complete. Once you move to the 2-hour + timeframe, to complete an athletic event, is when you need to be much more concerned with specific pre and race day nutrition details.
For more information, do a google search for “race day nutrition.”