The promotion runs all day on November 7th and 100% of the net proceeds of Slurpees sold that day will go to Feeding America to benefit local food banks. The idea here is on 7/11, 7-Eleven gave out free Slurpees and are now asking customers to give back (to their community) on 11/7.
There's no limit on how many Slurpees you can buy and no minimum price you must pay during the promotion (although you'll look like a huge jerk if you walk out double-fisting two giant Slurpees having paid zero dollars for them).
For those of you reading up north in Canada, 7-Eleven offers a slighty different promotion on the same day: the National Slurpee Beach Party. Simply show up to your local 7-Eleven in a bathing suit on November 7th, between 11 AM and 7 PM, and score a free medium Slurpee (Should be fun... especially if it's snowing out).
Slurpees purchased/received by 7Rewards (7-Eleven's free customer loyalty program) members count as a punch for the "Buy 6 Cups, Get the 7th Free" punchcard in the 7-Eleven smartphone app.
Photo via 7-Eleven.