If breakfast is the most important meal, that's never truer than on race day. But choosing the right fuel depends on the type of event you're competing in. "Your specific needs come down to the differences in the time and intensity you'll be going at," says Pamela Nisevich Bede, a nutritional consultant for Swim, Bike, Run, Eat. "It's also a question of what sits well with you, which you'll figure out over time." Here's what you should be eating and why.