Okay, I don't think this has been done before on this forum.
Well, you all know how to play Rock, Paper, Scissors, right? This is similar, but you aren't restricted to those same three items. Basically, you can use whatever weapon you like to beat the person before you, as long as you explain why your item wins.
For example:
Poster 1: Paper covers rock
Poster 2: Fire burns paper
Poster 3: Water quenches fire
etc
So, I'll start off with an old favourite for the next poster to beat: cookies!