I used to be an avid runner, although not endurance (usually between three and six miles since I used it for horse endurance training), which I hope to take up again this summer and I "skirt the margins" of endurance horseback riding, which is what I truly hope to do once I am done with grad school.
As mentioned above, stay hydrated. Additionally, I bring some type of nutritional bar during the ride. I take my medications at a very specific time (9 AM and 9 PM), which means they have to stay with me, but it's also a good thing in case I were to have a seizure on the horse and someone needed to know why I was having a seizure. I also notify other people than the person I am riding with that I am epileptic. I change out my helmet often because they don't last forever! I also sometimes ride with a safety vest-- I think that might impair cycling, but it is a thought.
I am also never alone. I actually think that this is imperative. Yes, a phone can help, but it can only help so much. In fact, while my epileptologist encourages the horses, he does ask that I ride with someone.
Lastly, I noticed that my particular AEDs caused me to lose some muscle, which did affect my endurance overall and when I switched medications I became very sensitive to heat when I wasn't before. I had to quit running for a while because I would get quickly overheated. Ha, now grad school is the culprit. I think it's good to be aware of side effects and note if you've been incredibly active and had high endurance and suddenly something does change. Hopefully your neurologist will work with you since they should in order to maintain your lifestyle.