Fuelling - short term energy
What do you eat for a short burst of energy, to provide an extra boost to fuel that final push to the top? The short answer is sugar. Sugary foods are easy to eat, quick to digest and result in a rapid rise of blood sugar - which quickly supplies your muscles and brain.
Eating a lot of sugar is not usually something a nutritionist would recommend
Hypoglycaemia and exercise
Eating a lot of sugar is not usually something a nutritionist would recommend. It helps to rot your teeth and the rapid rise in blood glucose is often followed by a rapid fall leaving you more fatigued than before. However this pattern occurs at rest (for example, if you ate a packet of sweets while sitting reading the paper). If you eat sugar during exercise, the rise in your blood glucose level is blunted and rebound 'hypoglycaemia' (low blood sugar) does not usually occur.
Good and bad sugars
So it is okay to eat sugar during exercise - but some sugars are better than others. Sugars are either intrinsic (where the sugar is part of the cell structure and bound up in the fruit or vegetable) or extrinsic (where sugar is added e.g. to make cakes, biscuits, ice-cream, breakfast cereals, fruit squashes, jellies, custards, chocolate and sweets). Both forms of sugar will give you an energy boost, but the intrinsic sugars come in their natural concentration and form (apples, bananas, oranges, pears, etc.) and with a selection of useful vitamins, minerals and fibre - so you get a better nutritional package overall.
Don't think sugars are the only energy booster. Some starchy carbohydrates are also quickly digested and produce a fast release of glucose into the bloodstream. So while a honey sandwich, ripe bananas and raisins provide a lot of sugar, the bread (white or wholemeal) for your sandwiches is also digested quickly. (Avoid using a lot of butter or margarine, since fat tends to slow down digestion of carbohydrates and delay the energy boost).
Water
Fluids
Even for short term activities you need to have enough fluid (either in you, or on you) to avoid dehydration. If you want to travel light, make sure you start off well hydrated. Aim to drink at least 500ml (approx 1 pint) water in the hour before you climb. Then, if you are only moderately active in cool conditions, you can get away without taking any extra fluids. Otherwise drink at least 500ml water every hour.
DIY Combination
Alternatively, you can take your sugar boost and fluids in one drink. Diluted fruit juice (1 litre orange, apple, grapefruit or pineapple diluted with 1 litre of water) is a perfect energy boost and hydration fluid, all in one!