Potassium....
Often overlooked by athletes and bodybuilders. The RDA is only 4 grams which is a very low to start with. That's more than 15 bananas. It's almost impossible to eat enough to even reach 4 grams.
If you take a brisk walk or lift weights for 20 minutes you can burn through 4 grams fairly quickly. Which means you'll need to consume 8 grams to just break even. Most athletes, bodybuilders or anyone who works in a hot environment will need far more than that.
Make sure to balance it with some natural sea salt, calcium, and magnesium....