As one of my 7 ideas I submitted to this former client (1218 was what I put them all under in my list), this is one I'd use myself. Idea is to have gift cards to stores that have another brand printed on them. Specifically I was thinking of people who give gifts to others, and this could allow people to remember who actually gave them the card. Easy to do, but not sure what it would cost to print. Might just have stickers to slap their logos on, or leave a blank space and let the users buy their own stickers and then do it themselves.