Get a photocopy of the affy then you send it via some sort of mail system that tracks the package. It would be my luck for my affy to be on a plane that crashes or a truck that burns up, lol. You need the receipt to prove that it was sent and what happened to the affy.
The exeption is if the affy is for a cheap item. Sometimes a sponsor will want a simple form filled out and returned. I would not spend $7 to get a $3 coffee mug.