The way you approach your nutrition during the lead up to the race can be as important as your training. By this I mean that you can give yourself an edge, you can maintain your baseline, or you can completely mess yourself up.
My recipe for pre-race fueling includes eating very healthy from the Monday to Thursday before the race. This usually means either eggs or oatmeal for breakfast, a collagen-whey protein smoothie for lunch (with coconut milk and frozen berries), maybe a veggie wrap for a snack and then a veggie filled dinner with some good carbs and lean protein. I don't try to limit the amount of food I eat, but I also try to eat a reasonable amount.
I only race with Maple Syrup for fuel...
On Thursday I usually have an easy training day. This will coincide with consciously easing up on my diet. If I'm hungry, I'll have more carbs, or a chocolate chip cookie or something else that makes sure that i'm leaning to the side of over-fueled, instead of under-fueled. I don't go crazy, but I probably eat 300-500 extra calories on this day.
I do a similar thing for Friday, except around 1pm, I start to focus exclusively on foods that I digest really well. I'll stay away from salads, excessive amounts of vegetables or fruit and just have a bit more easy to digest carbs. For dinner on Friday, its mostly carbs, with a bit of protein and veggies only for taste. The reason I do this, is that eating any vegetables or fruit isn't going to help me race. In 12 hours, the slow-digesting nature of extra fibrous food will just be in my gut. The same goes for meats, so I just make sure to limit my intake. I drink a serving of BeetElite around 4pm and 8pm I go to bed satiated, but not full.
Usually I wake up at 5am on race morning and eat a bowl of oatmeal or white rice, with almond butter and coconut oil. Then coffee and BeetElite. Around 6:45 i'll have 1/2 a banana and 1/2 serving of BeetElite. At 7am i'll eat a gel, and sip on some water. Then its off to the race start at 7:30am! I only race with Maple Syrup for fuel. I find its delicious and works better than the stodgy gels from Clif, GU or any of those other companies.