Get a Free Slurpee @ 7-Eleven with this printable Voucher
Apparently, you just go to the website, click "Join now" under "Become and Official Slurper".
Then fill in the required details. You need a valid email address to receive the voucher.
Finally, print out the voucher and present it at the nearest 7-Eleven Store to claim your free slurpee.
Doesn't indicate an expiry date.