Start by cutting a hole in the box for your child's head. Or, if the box is smaller, then you'll attach straps to the edges of the box when the costume is completed (like suspenders) and fit them over your child's shoulders. Also, cut arm holes if you aren't doing the suspender method. Then you're ready to get started. All of these outfits fit perfectly over leggings and a long sleeve shirt (or jacket).

A Wrapped Gift
Wrap the entire box in gift wrap (whatever kind you like the best) and stick a bow on your child's head. He or she can trick-or-treat as a wrapped gift.

Computer Monitor
Spray paint the box grey. After it dries, paint a white screen on the front of the monitor. Of course, you can have fun decorating the screen with your favorite website, or print the screen from your favorite website and glue it onto the box for a more realistic look.

Box of Cereal
Does your child have a favorite cereal? Fruit Loops, Cheerios, Cocoa Puffs? Any box of cereal can be painted onto a cardboard box and turned into a costume.

Robot
Spray paint the box grey or silver. Then, after the paint dries, find a mish-mash of nuts and bolts and glue them to the box. You may also create attachments from aluminum foil, dryer vents, duct tape, or whatever you have lying around the house.

Invite your child to help with making his or her costume. Spending time creating these costumes together may end up being even more fun than trick-or-treating. Be sure to take lots of pictures.