For people that think you can combine it with another coupon, you can't.
BB's register system automatically cancels out any coupon used on a transaction when another one is applied, so you can't use two different types of coupons at once. You can use multiples of the same coupon, though not two different types.
RZ Certs are considered payment, so they don't cause issues with coupon usage.
You might luck out and have someone manually change the price on a game to have a coupon work, though any manual price changes also nuke any coupon usage.