I’m a distance runner who trains fasted. You’re on the right track with practicing fueling for your upcoming event. I definitely fuel for races (although I ran a marathon last fall on almost zero calories just to test it out…went great!). Most people seem to choose a gel, the chewable gel blocks, or a waffle-type fuel. If you’re used to training fasted, you likely won’t need much, probably no more than 100 calories/hour, which will give you a good energy boost. I use Huma gels when racing, and I don’t need the first one until I’m at least an hour or more into the race. (My pre-race fuel is a cup of black coffee.). As you’re trying things, note which type of sugar it has, so you can identify if your stomach has an issue with certain sugars. And if you want to fuel with something with less sugar, a nut butter packet (like Justin’s) is a good choice (1/2 packet at a time), or cashews. There’s also a product called UCAN that comes in a drink, bar, or gel paste which is pricey, but a good, effective fuel for fat-burning athletes as it doesn’t spike blood sugar (so you can continue to burn fat for fuel, plus benefit from the carbs in UCAN.). Good luck with your training and ride!
If you have train fasted i would probably just do it fasted. You have the energy coming from fat so you should be just fine. I would take an electrolyte drink and maybe a small backup snack if needed but thats it.