Fueling your body is important regardless of the exercise you undertake but distance running means you have to pay particular attention to it.
For runs of an hour or more, you’ll be using fuel from your glycogen stores (i.e. carbohydrates) so you’ll need to keep topping your carbohydrates up.
Ascertain which drinks, gels and snacks will be available at certain points during the race and calculate if they’ll work for you. If they’re different to what you’d normally consume
A few days before the race, begin to carb-load (increase your carb intake) to ensure a constant fuel source.
On race day, stick with what you know agrees with your body.
During the race, continue with your hydration and carb refuel plan. Hydrate with about 250ml liquid each hour plus 30-60g of carbs (the amount will depend on your weight and body composition). Endomondo is a great running app which tells you how much water you should’ve taken on during your run. Certain sweets are better than others; many runners swear by jelly babies as they don’t tend to stick to anything (I guess that icing sugar coating *is* there for a reason after all!) and they kind of melt in your mouth without too much chewing. I tend to take the small bags aimed at children to stop me eating too many. During training, decide whether you’re going to eat one every minutes or after a certain distance.
Remember: stick with what you know!