Wear a black skee mask and a black turtle neck and black jeans. Also a black bandana. Hold a sack that is also you're trick-or-treat bag. Wear dark shoes. Have fun!
Thanks to Giulia for this good idea.
Another great idea is a, ROBBER!!!
Get a black and white striped shirt and black pants. Get a ski mask and what do you know... a robber!
Thanks to Kristen for this addition!