So, this is a pretty weak hustle, but if you're around an unattended machine....
Get the Coke Freestyle app. Make a custom drink and save it. Go to one of those mix your own combination Coke fountains. Scan the QR code on the machine, select your custom drink on the screen, tap the pour button, and walk away. Every 5 times you do this (limited to once per day) you get a $5 Amazon gift card, limit of 2 cards in March.
I walk through a food court on my daily Pokemon Go route, so it's pretty quick and easy. The employees at Chik Fil A are starting to look at me funny but meh.