The first thing to realise is that on a challenge like this you're going to be burning calories like there's no tomorrow! Whilst that may sound great if you're on a diet, you still need plenty of food for energy. That's the most important thing. Three days of constant exersion is a killer.

The main thing is you should eat often, and tons of it!

When you're travelling between locations try to eat loads of carbohydrates (rice, pasta, potatoes etc.), along with plenty of protein (chicken, turkey, tuna, steak etc.) Add as much vegetables to that as you can as well. Preferabley green vegetables as they generally give you more nutrition. Brocolli is a good example.

You could pre-make a huge chicken, noodle and vegetable salad for example and take it in a big tupperware. Or try to stop in places with "All you can eat buffy's" and eat like a horse!

On the hill it's more or less the same, carbohydrates! Sandwiches, rolls, bacon butties, pork pies, cornish pasties, whatever takes your fancy really, but save that for the rest stops. Along the way, tuck into dried fruit, nuts (salted ones are good because they replace lost minerals through sweating), mars bars, smarties and anything else you really like.

If eating big meals is a problem you could buy a few meal replacement bars. These have the same amount of calories (and goodness?) as a light meal. The beauty of these is that they don't make you feel full or bloated like a proper meal would. You can also buy it in powder form which you mix with milk or water usually.

You can also get loads of extra calories from drinking full fat milk. Don't worry about the extra fat content. Your body has bigger problems to deal with.

A few energy bars probably wouldn't go amiss either for that last push towards a summit.

Water! Even more important than the food? Probably.

Drink as much water as you can! I'll say that again... Drink LOADS of water, especially if you're having a few beers along the way.

Have a great time, and best of luck with the challenge!