My races are somewhere between 3 and 10 hours long. Regardless of whether its XXC, Marathon, or NUE, they all require many hours of top performance from my body. I've tried many things during races, and what I've learned about my body is that after a few hours, it begins to reject hard foods. When you're 5 hours into a 100 mile NUE race and you can't stomach the Probars you have in your jersey, you're in trouble. I had that exact thing happen to me this year at the Cohutta 100. After that race, I began looking for better solutions.
Your body needs to replace what it is losing while you race. Some say that a good rule of thumb is 300 calories an hour intake is needed to replace what you're losing to keep you fueled enough for top level efforts. But any old 300 calories won't work, you need specific types of fuel.
Since races are all different lengths, I'll break it down generically. In the beginning of a race I try to make sure that I'm getting in some caffeine and liquids. I typically try to consume 20-24 ounces of water an hour. By using Infinit Jet Fuel, I can get the liquids and the caffeine all at once. The middle of a given race is when I want to have some more sustenance to make sure I'm never getting hungry. I'll continue drinking Infinit, but I switch over to Go Far for my calories. I'll also throw in a few Powerbar gels to keep my sugar consumption up. Towards the end of a race, I'll be feeling depleted no matter what I do, so I switch back to Jet Fuel for the last push I need to get through to the end.
Even when my body is in full reject mode of food, it is still willing to take water and gels. As a result of learning this, I've built this plan around those two as my baseline. Thankfully, I can get the calories I need every hour from Infinit and Powerbar. I mix Infinit into water bottles that I pick up during races, and I even mix the gels with water and put them into a flask for ease of eating on the trail.
The most important part of endurance nutrition though, and I cannot stress this enough, practicing your nutrition during training. Race day should feel like training, not an experiment with things you are unfamiliar with.