I always ride with 2 water bottles (which I will freeze part of before the ride if its going to be a hot one, so you can add water to it and it keeps it chilled while on trail).
I used to ride with a bottle of gatorade or some other "sports drink" in place of one water bottle, but I hated the chemical taste and would have to cut it by 1/2 or even 2/3s with water before I could gag it down. That worked ok for some 50s.. but once the temps went into the 90s or the ride distance increased past about 70 miles, the migraines and accompanying dizziness and shakiness would start.
In asking around, I found out a lot of people were using capsule-form electrolytes meant for human endurance runners. I was skeptical, as I have a weenie stomach during a ride and it doesn't take much to make me feel sick. I figured as soon as the capsule dissolved, I would be puking. But after trying every drink imaginable and having nothing work, I figured what the hell. I do eat a granola bar as a chaser (they are one of the few foods I can consistently eat at a ride) just in case, but I have never had even a funny feeling after taking the elyte capsules.
What a difference!!! Not only did it keep the migraines at bay, it actually dramatically reduced and in some cases stopped the after-ride muscle soreness. I rode the OD 100 last year with no soreness at all after the ride, then did a 2-day 100 the following weekend and again had no even a twinge. I would never have believed it!