Caffeine is one of the few supplements with strong evidence for improving endurance performance. A dose of about 3–6 mg per kg of body weight, taken around 60 minutes before exercise, can make hard efforts feel easier and help you sustain pace for longer.
The best fuel format is the one you can carry, stomach and take on reliably at race pace. Most athletes do best with a mix: drinks for fluid and electrolytes, gels or chews for concentrated carbs, and real food for longer, slower efforts.
Your gut is trainable, just like your legs and lungs. By gradually increasing how much carbohydrate and fluid you take in during training, you can improve absorption and cut the risk of stomach problems on race day.
For most endurance events, aim for 30–60 g of carbohydrate per hour for efforts of 1–2.5 hours, and 60–90 g per hour for anything longer. Some well-trained athletes now push to 100–120 g per hour, but only after deliberate gut training.