The "Share-a-Slurpee" offer is good on any size and flavor Slurpee at participating locations nationwide (stores in Michigan are specifically not participating).
The convenience store chain's current featured Slurpee flavor is Cap'n Crunch Crunch Berries.
As an added bonus, during the promotion, both the purchased Slurpee and the free Slurpee count as a point each for the chain's mobile app 7Rewards "Buy Six, Get the Seventh Free" drink special.
Photo via 7-Eleven.