Coffee heads, stop using your Starbucks and Dunkin' cards. Square has an app called "Cash" that recently just brought out an insane deal. (This app is very similar to what Venmo is).
Basically, if you have the app and use the card that they send to you for free, any coffee purchase of $1.50 or more gives you $1 back. Only limitation that you can only redeem this offer 10 times a day. I know... insane. It honestly beats out ANY coffee loyalty program. Most force you to spend a considerable amount before you even get a free drink.
Obviously brewing your own is the cheapest, but this, in my opinion, beats out any deal I've ever found.
More info here. [squareup.com]