Actually gatorade and most of the other sports drinks, have a very small amount of electrolyes (check the back - 2 or 3% or daily). Coconut water is all the rage for Potassium these days. It is relatively now in calories, unless you get one of the amped up flavored varieties, but loaded with potassium.
Whole fruit is probably your best bet overall for a balanced electrolye profile.
I am one of those rare people who have trouble getting enough sodium when I am training for long races, so I actually injest regular table salt. On runs longer than 10 miles in the summer I take along those little packets they give you for take out. They are about 750mg (.75 g) and will relieve electrolyte-induced foot and let cramps in seconds.
2.5 years, 45 pounds later... 128ish pounds