I use Sqwincher lite Kwik sticks. 0.1oz, designed for 20 oz bottles, works fine in about a liter. I get them from work, they are sold mostly by safety supply companies today.
Small amts of electrolytes, but I dont really even use them for electrolyte, Its mostly for a little bit of flavoring to water, I drink a lot more water that way.
I tried some electrolytes, that tasted pretty bad IMO. EmergenC, Nuun, the taste was not conducive to drinking, in fact, it worked the other way. I didnt want to drink it, so I drank less.
I have picked up any of the wide variety WalMart sells in a pinch as well on the way to a trailhead. Liquid too. Cant say I think Ive ever suffered electrolyte deficiencies.