I have some friends who own a cupcake shop--so, for no particular reason, I decided to make a talking cupcake.
I scanned a cupcake, then split it into a top and bottom half. I hollowed out the bottom half and adjusted the parts to accommodate motors and electronics. Electronic construction details are available on instructables.com
This has a 20 second limit on the recordable message (change whenever you like) and it plays whenever someone walks by. You could make a sandwich or any other talking advertisement item you choose. http://youtu.be/o26WH8pdd1A