We're still on our ghost theme because that's what my two have decided they want to dress up as for guising this year. Need to go and check and see if I have any old white sheets that are ready for decluttering...
Take your paper cup and make a small hole in the bottom. The safest way is to take a lump of plasticine, put your cup on top and push through using a pair of scissors or screwdriver (or chopstick, if it's a papercup).
Draw on a couple of eyes and your ghost is ready for takeoff ;)