90210. Since you're only in high school, you don't remember Shannon Doherty, whatever show she was on pre-90210 barking, "Pasta. I'm running tomorrow." That stuck in my head when I was younger because it seemed like such a weird thing to say.
Turned out, the show was trying to educate viewers (or at least give Shannon Doherty a line she could bark). Complex carbohydrates are great for people who are running or working hard, so if you're feeling tired, you should start eating whole-wheat pastas the day before a big event. This will help give your body the complex carbs you need to get out their and kick it.
Try Some Green. Robert O. Young wrote the book The pH Miracle: Balance Your Diet, Reclaim Your Health.
In his book he writes about the importance of a high alkaline diet for athletes. This means eat your vegetables.
What is really awesome about this approach is that you will have energy and power way before you need to perform. It's sustained, you will have stamina. You will even study better because your body is fit--through and through.
Complex Carbs before Competition. Pasta, unsalted crackers and other complex carbs are a good idea before competition. However, I've heard that athletes should be careful not to consume them too close to the start of the competition, as that can make you feel uncomfortable once you've begun the activity. About three hours before, a carb-rich meal, with a lean protein, is a good idea.