Actually - you could just get a large square box, paint squares on it and go as a rubik's cube?
If you want something 'scary'
Mummy : Wrap yourself in white bandages. Use splotches of green paint for "mould". Use white make-up on face with "age lines" drawn on. The stiff-legged gait works perfectly.
Cereal Killer : Attach little cereal boxes to a shirt, cut a slit in the boxes, glue in plastic knives into the holes, drip red paint running down from the knife hole in the box.
more here:
http://www.robinsfyi.com/holidays/halloween/co stumes.htm