Summarize:

A breakfast that is rich in carbs is ideal. This will give you a vital energy boost and prevent you from going hungry later in the day. A donut is a carb, but you can do better than that. Avoid a lot of sugar and high fat proteins. Cereal, milk, and a banana would be a good option. You don't want to show up to the tournament with a growling stomach and realize you don't have anything to eat. Pack something like a sandwich and fruit for lunch. For a snack, things like nuts, bananas, granola bars, and dried fruit are ideal. Keep snacking up until right before the tournament, but don't get too full. All of this food and drink will keep you energized during the tournament, and will help you play the best you can. Make sure to bring a refillable water bottle. Nap for about two hours before you leave for the tournament, and make sure to set an alarm. You definitely don't want to wake up and realize the tournament has already passed. A nap time of about 20 minutes would be ideal, though you can adjust the time to your liking. A short nap will give you an extra energy and performance while you play. Accidents and traffic are impossible to control, but it would be a good idea to do everything you can to prevent showing up late. Map the location of the tournament before you leave. It wouldn't hurt to plan a few alternative routes as well. Leave for the tournament with so much time to spare that not even a fallen tree, traffic accident, or stop for gas could make you late. Being nervous will only hinder your performance, even if it is normal and expected. Take a moment to step aside and sit back. Reflect on all of the hard work that led you to this moment. Close your eyes and meditate. When your thoughts have steadied, get up and get prepared to win this game. Your mind might be racing before the gamethinking of past and future games. Resist the temptation to dwell on anything except the present moment. Don't think about what this tournament means for your future in the sport. Just think about how you can be the best you can be. It's okay if your mind drifts. Recognize you're doing it and refocus. You shouldn't overdo it, but it is important that your body is prepared for what its about to endure. Run a few laps. Stretch your muscles out. Do whatever you have to do for your particular sport. Then all that's left to do is have fun.
Have a big, healthy breakfast on the day of the tournament. Pack a healthy lunch and snack. Take a short nap. Arrive on time at the venue. Relax. Don't get distracted. Warm up your body.