I hope not, because the one from Avis is pretty useless. It's short-expiration free 2-day weekend rental certificate, which do not include all taxes and fees, do not include any insurance (but at the same time make credit card collision insurance unusable), and you have to pay for anything beyond two days, and you cannot use them without a "Saturday stay". And btw you don't earn any free rental points or certificates, at most rental agencies, if you earn airline miles (or hotel or rail points) on your rentals.

In fact, you should also look into using airline miles for car rentals. That's possible with several of the airlines. And it's quite likely using miles would pay for the rental "more completely" than (at least) one of these very limited certificates that Avis issues.