A Magical Memories certificate is given out to guests for special "events". We have gotten them several times, both at WDW, and on the ship. We were the 100th Family in The Plaza Restaurant, so the Mayor came in, made a big announcemnet, had pictures taken, and was given the certificate. On the cruise my kids got one for being the best pin traders on board. The CM's do it to make your vacation more magical. My kids love getting them. I am pretty sure it is a random thing, and that you cannot buy them.