Food is hard to manage while training let alone while racing in an event. It is worth trying out different varieties and recipes to find out what works for you. I run with a lot of people who steer clear of processed foods and eat a lot of fruits and even raw foods during a race. Personally I get my carbs anyway I can from a 100% vegetarian diet and seem to able to stomach most of it. I like eating anything that is tasty and healthy (or sweet when necessary) and find it can be motivational in a race. Running to the next aid station or food delivery can keep you going. For some ideas of what I ate in the 3100 visit my article on running and nutrition.

As far as supplements go, in the 3100 I was taking Vitamin C, Calcium and Magnesium, Pantothenic Acid (B5) and a Multi-Vitamin and slurping a protein shake once or twice a day. I don't take any supplements when training and some of the pills mentioned above are the size of horse pills, thoroughly unenjoyable to swallow! Supplements can be a major expense so you need to factor them into your budget and judge whether they help you or not (Finnish ultra running legend Asphrihanal Aalto doesn't take anything at all). 

Grahak Cunningham is a motivational keynote speaker and four time finisher of the 3100 mile race.