simple enough, hand the next poster an item, or object, or weapon, or whatever. then they do something with it, and give the next poster something else.
A:the next poster gets a scimitar.
B:*fights off the Persian army*
next poster gets a tool box.
C:*uses tools to build a lifesized fully operational gundam*
next poster gets the gundam.
so to start this off, the first poster gets a lotto ticket.