If you do not already have a Cainiac Club card, you will have to go to your restaurant location to get one. Then you will need to register your card on the Raising Cane’s site to get your free box combo.
I remember when Raising Cane’s first came to College Station (Gig ‘Em Aggies!) they put out the coupon for a free combo meal in the coupon book that they give out to the students at the beginning of the semester. Needless to say, we got A LOT of free chicken that semester!
To see all available restaurant coupons visit the Restaurant Coupons Database! (now optimized for mobile devices!)