Ditto, the "some sugar" suggestion. Helps with osmolarity in rehydration. That's why Ringer's lactate is often preferred over normal saline for dehydration, and it's the theory behind the formulation of DripDrop ORS, a powdered electrolyte advertised as an oral rehydration system, as a second choice substitute for Ringer's when an IV is impossible or impractical.
I've used just about every commercially made electrolyte recipe -- readymade drinks, powders and tablets -- and DripDrop is the best I've tried. They explain on their website tech section why a small amount of some form of sugar is essential. There's nothing magical in DripDrop, but they've nailed the right balance of ingredients. And it comes in waterproof Mylar packets, easy to tuck into any saddle bag or jersey pocket. Tastes good too, not too sweet, no bitter or cloying aftertaste, and has some amusing flavors like watermelon.
If I had to make my own from readily available stuff in the kitchen, I'd use Morton's "light salt," a mixture of sodium and potassium chloride, and table sugar or any other form of sugar -- sucrose, fructose, glucose, dextrose, doesn't really matter. Since I already have various supplements containing magnesium and calcium, I'd add a pinch of those.
Ditto an antacid containing a bit of citric acid -- Picot, popular in stores in Mexican-American neighborhoods, is handy for adding to a homebrewed sports drink. It contains citric acid, sodium bicarbonate and sucrose, all handy for sports drinks.