I actually enjoyed the coupon thing by Avis. For the following reason:

Since I am preferred, the car always waits for me. I put various coupon codes into it (like One Free Day, and the like), and always it gets minused from the total, so I don't have to go to the counter, and usually I can keep the coupon (except for JFK location).

For example, I had the coupon that is given to first-time Chairman Club renters for five-day free rental, and I used it two times.

I used two "free day" certificates four or five times.

I used weekend-er certificates few times (before they became electronic and they started keeping track).