Back when I worked at UPS in the sort facility, I used to get a cheap electrolyte powder to mix in my water. It had potassium, magnesium and sodium (although I was just looking on Amazon to try to remember the brand and they may not sell it any more). At the time I was on a medication that made me sweat profusely so it became pretty critical. I found that I couldn't get enough potassium from food alone to keep up. There seem to be a lot of options out there.