For me it is important that supplements are functional and the sportsperson understands why they are being used. Taking a food first approach is essential. During exercise lasting longer than 30 minutes it will be important to rehydrate with between 200-500 mls of fluid as regularly as possible. Water is suitable beforehand, but during is when isotonic drinks have been proven to be effective. The mix of electrolytes and glucose gives a dual benefit, with energy boosting effects and reduction to the risk of cramps.
Raisins, blackcurrants and mango are great half time foods, for half way through to provide a perfect boost of fructose sugar in the bloodstream. Myths around taking fat burning tablets and so on still survive today but the best thing to consume is high quality food and drink. World Anti Doping (WADA) guidelines state we should be careful with any dietary supplement. Check this out with a Registered Dietitian before considering any supplementation. Focus on eating real food and then understanding if there are any deficiencies in the diet before looking at if additional help is necessary.