I have seen Bank of America credit card sometimes offer a extra bonus cash back for Autozone, something like 5% if you use their cc. But you need to register via their website first. Not sure if promo is still active or not.
Ya retailmenot has all kinds of coupons. I always check with that site before ordering online. Sometimes they have allot of outdated stuff, which I have tried and some stores will still take it. When I order stuff from dog.com or diget pet.com, they always have great codes that save a bunch of money. But autozone I think is more into the member card that after 5 purchases over 20 bucks and you earn 20 bucks.