Remembering to breath and try to relax on the sections instead of griping the handle bars and brakes as hard as you can is my tip for energy. You get so worn out if your tense all the way through a section.
Other than that I eat a bannana or two through the day, chocolate and lots of water.
I try to avoid eating too much "sit on your stomach" foods like sandwiches or pasties till after the last section.