I have a handy dandy little thing. It's called a coupon bag. That's where I put my coupons. Rarely do they get lost.

I also mentioned a handy dandy thing I also have in my response to the Ace Storage whine. It's called a calender. Where I note payment due dates I also note exp dates on said coupons and I radical idea here, go there before it expires.

Costco also keeps track of what you buy. You could have called to explain you lost your coupon.