Avid road cyclist here; as I type this, I am drinking a recovery drink immediately after a 80 mile training ride (
https://www.strava.com/activities/2308407367). Did three 100+ mile events last year and rode 531 miles in 8 days for RAGBRAI last summer. I only say all that to really say: I've learned the hard way what works for me, YMMV. You've kind of got three problems depending on what you are doing: hydration (keep up blood pressure), electrolytes (water is not always enough) and fuel (calories in a form that will not upset your stomach).
I have not DIY'd a sport drink--I think there's a lot of science behind the good commercial ones and they aren't super expensive. Plus, hitting all three needs above isn't simple in a way that you can tolerate. I have found that fueling properly is actually the biggest challenge people have as they progress from casual exercise to something more endurance (more than an hour?) in nature. Too many simple sugars will lead to unhappiness.
There are some powdered drink mixes that conquer all three, like Tailwind Nutrition, which I really like for anything 1-4 hours in length. For 1-2 hour events, Gatorade or Gatorade G2 works well (it's light on the fueling side, but is less costly calorie wise). G2 is also easily available in almost any grocery store.
Hammer Nutrition is my Go To for just about anything. HEED is a fantastic 1-3 hour drink mix that addresses all three needs. For longer than 3 hours, Hammer's Perpetuem is the best fuel, period. I have never bonked with it (bonking really sucks, bad). So, to get at all three needs for long events, I use Nuun tablets in my water bottles. Maybe a few gels thrown in for good measure. I really like Sport Beans (Jelly Belly) and Stinger Waffles too.
I've got my first century ride for 2019 next weekend, so we will soon see if I still have a workable plan! BTW, I am shy on donations to enable riding next weekend (each participant needs to raise a minimum of $200). If anyone is so inclined,
this link would be great for anything you all would like to contribute--any $$$ amount is fantastic.