Limit high fibre foods, i.e. bran muffins, added bran cereals and breads, and fibrous raw vegetables, especially prior to events longer than two hours. During the event or exercise Generally, if the exercise or event you are in takes 90 minutes to 2 hours you'll probably only need to replace spent body fluids. Don't wait till your thirsty, it takes 15-20 mins for your body to utilize the water you just drank. Its easier to find a tree than the first aid tent. If the event is longer or you feel fatigued earlier, you'll need to replace the spent carbo energy.
Most athletes usually turn to commercial replacement drinks.
Fresh fruit and their juices, plain or enhanced water is best, commercial liquid supplements are O.K. if you like them. I personally recommend watered down fresh juice. Most commercial drinks are based on the analysis of body sweat and made to replace the components found in sweat. The body's skin is the largest organ of elimination and the sweat doesn't truly reflect the needs of your internal cells, energy systems or musclular needs. A neat trick is to make soak water, that is, soaking dried fruits such as raisins, dates, etc.