Very clever. I can’t tell what the backpacks are made of, but the proton guns are Uzis. The kids’ names are sewn on the uniforms.
UPDATE (10/23/13): Nick sent me details regarding the costumes:
The costumes were built with a pattern that had come out during that year for costumes. The backpacks were simply spray-painted cardboard boxes with shoulder straps. However, a special opening at the top allowed people to drop candy inside, so we could have theoretically mopped up some serious candy because the boxes could hold a lot. While we never got a photo of the rear of the backpacks, my brother designed the outside with all sorts of hoses and accouterments so it would have a “wow” factor that made it look very fancy and techie. The Uzis were just the standard toy gun from K-Mart that you could buy at the time. Through standard rubber hoses, they were then attached to the backpack.
(Photo via nick_cw1861/Flickr)