Just chiming in here to offer my advice from professional experience. I used to exercise a lot when I was younger. I did triathlons and a few half marathons. Hydration is extremely important and often it is ignored. Your body needs water to function properly, plain and simple. Your body uses an incredible amount of electrolytes in heat and strenuous activities. A great source for this is actually pickle juice, but if you are like me and don't want to drink a jar or pickles, there are plenty of other options. I used to make a drink for myself that was actually pretty good and worked great. A mixture of water (duh) lemon juice, coconut water, mint, baking soda, and a tiny bit of salt. But just remember, what you take it, has to come back out. I thought about using one of those hydration packs and it would be a great idea but as others have said, using the facilities makes it a pain. You could always get yourself one of those stadium wizzers though