Long runs are the perfect opportunity to practice your race day fueling plan. Practice what your going to eat and drink before and during the race. What, when, and how much depends on the distance and time you are running, along with what your tummy and GI system will tolerate. What works for one person can be completely different than what works for another. Thankfully there are many different options and products to pick from and try.
Recommendations for fueling before a longer race are to aim for 50 grams of carb for every hour you're eating prior to the race. So for example, if it's 1 hour before, you should consume about 50 grams of carb; 2 hours before, about 100 grams; 4 hours before, about 200 grams. Eating a little protein and fat is good too, just not too close to starting. Tomorrow, 2 hours before I head out for my 20+ miler, I'll drink some Tailwind and eat a Honeystinger waffle. Then an hour before, will eat a large banana. This will mimic my pre-marathon intake as well.
As far as for fueling during a run, for runs lasting longer than 60 minutes, you should start taking carb at the half an hour mark, aiming for 30 to 60 grams of carb per hour. I have found that my tummy does better when I alternate gels. I will take a Honeystinger then Maurten gel and so on every 4 to 5 miles. I carry a water vest and will drink water from that with the gels. While the Maurten gels say they do not need to be taken with water, this is how other gels are designed to be consumed. Not taking then with water can lead to GI distress.
In order to replace electrolytes lost via sweat, there are many drink options out there like Nuun or even Gatorade. My tummy does not do well with electrolyte drinks during running, no matter how many times I've tried. I am a heavy sweater though so I do need more electrolytes than what the gels provide. In order to replenish those for myself, I have found taking the saltstick fastchews work well.
It looks like a lot all laid out, but in order to perform my best, I know I need to be adequately fueled. And for me, after lots of trial and error and experimentation, have found this variety is what works. If you are struggling to find how to best fuel your own runs, or just beginning your journey and would like some direction, I would love to help.