Person one puts something into the vending machine. The next person to post says what the machine gave the poster before them then puts their own item in for the next poster to say what they got from the machine.
Ex. (person 1) I put a puppy into the vending machine.
(person 2) You get a blind lizard.
I put an old tire into the vending machine.
(person 3) You get a brand new Honda.
I put...
I put $200 into the machine.
You get a bag of nails.
I put a Cool Stranger Hat into the machine.