Besides being an effective mild stimulant, caffeine also immobilizes free fatty acids for use as a fuel. This has a glycogen sparing effect which reduces fatigue. Care must be taken to avoid dehydration since caffeine is a diuretic, requiring an increase in water consumption. Drink only bottled water to avoid any possible water-borne bacteria which could cause illness. My support crew purchases the water in multipacks of liter bottles before the start.
Common sense is the best advice on food selection.
Foods should be easy to obtain and tasty enough to maintain the rider's interest. Give in to cravings as the body sometimes senses deficiencies in substances. Always carry some food between the controls. Navigating on strange roads at night is not easy, so the use of a cycling computer that displays kilometers is essential for anticipating a turn or a control. These are small, light, and easy to clamp on in a variety of ways and are fairly easy to open for battery replacement.