Have a 7-Eleven nearby? Download their Free iPhone or Android App. Once you log into the app, click on special offers or the dollar sign. You should see a coupon for a FREE Small Diet Coke Frost Cherry Slurpee, which is valid through 4/1/14! Be sure not to tap the “Redeem Offer” button until you’re in the 7-Eleven store as it only lasts for 15 minutes after that!