Nutrition & Hydration
This is an area that is broken into before, during and after a training run, and also on event day. It is similar to triathlon, although you tend to rely more on solids in a triathlon for the non-pro athletes, due to the day being longer. But that does depend, naturally, on the length of your run. There are so many variables, as logic would suggest you won't need as much fuel for a 10km as you do for a marathon.
“If you don’t eat according to your goals, don’t expect to reach them.”
Find What Works
It's a real science as things like sweat rates, glycogen stores and depletion rates, glucose intake, protein Vs carbohydrate etc all play a part as to how long the engine can go for. It can be info overload but in short, trial and error.
What works for you, probably won't work for the next person. It's a very individual thing and there's not a 'one fix all' solution to nutrition and hydration. Once you find what does work though, stick with it.