Nuun is good stuff, but way to expensive for everyday use, really a splurge for me.
I run trails in 100F or near temps almost daily during the spring and summer, Gatorade is inexpensive, readily available, and works just fine. I go with the classic Lemon.
I'll usually run with 2 handhelds, fill one up with water, and the other with 2/3 Gatorade, 1/3 water.
At the trailhead after a run, I replenish with water and Gatorade... like I said it's cheap. Not the best tasting for sure, but Eric hit it on the head, after a hard effort, whatever it is you're doing outdoors, anything besides just straight water.