G.B.
Cowboy, jeans, belt, long sleeve shirt. Boots if he has any.
Ghost, old sheet.
Mouse, gray sweat pants and shirt. Add black triangle nose and a few whiskers, can put some fake ears on from Walmart. I wouldn't worry about a tail if you can't buy one quickly.
Cat, same as above but different color sweats.
Put a big name tag on and be a game show contestant. Can dress crazy if that's part of their personality.
Get an orange tee shirt and some sticky back felt. Be a jack O' lantern.