In reply to drunken monkey:
That isn't too far, so eating shouldn't be a problem. Don't try anything new, like gels, energy drinks, juices etc. which you haven't practised with. Stick to plain and simple, sandwiches, cake, malt loaf (I spread butter and marmite), choccy bars, banannas, plus some savoury/salted like salted peanuts, cheesy crackers, and make sure you have handfull of jelly babies in case you need a sudden sugar boost (you'll know if you do).
No need to take masses, just ensure you have both sweet and savoury available and keep nibbling little and often. Drink wise, if in doubt, stick to plain water - it's kept humans alive for quite a few years so it must work!