Give each contestant (up to 16) a number. Then press the button and give the winner a prize. Like a private island. Or a self-driving car. Or, if you're a teacher, maybe you can give out a pencil.
All by me. My mom needed this so she could pick a random winner for her contest. It turns out there were 87 CONTESTANTS!!! So I made her a (not so good-looking) version right here: http://scratch.mit.edu/projects/16260619/