Salts, as mentioned (electrolyte balance). Also MAGNESIUM is CRITICAL. Vitamin E (not synthetic, as it is a scam). Some times calcium too, but rarely are people calcium deficient these days.
Magnesium is actually very hard to correctly test, as only 1% of the body's magnesium is in the blood. I think the true magnesium test is called intracellular magnesium levels, or something like that, and only a few high tech places in the world do them.