Most marathons start in the morning, and you don't have time to digest a big breakfast, but eating something before the race helps jump-start your muscles and calm a nervous stomach. Your best bet is to eat what you usually eat before your long runs. Try a banana with some honey and a cup of tea (also with a bit of honey). If the race is later than 10 a.m. and you ate early and feel hungry, snack on an energy bar an hour or so before the start. Drink some water, but resist the urge to over-hydrate. Even on a hot day, your body can only process so much, and you don't want to make excessive pit stops during the marathon.