hey there, sounds like a great party.
when i worked at a fabric store, we took pieces of cheese cloth and dip in a mixture of cornstarch and water, squeeze out eccess mixture and make the shape of a ghost by draping over a glass, jar, or whatever you have around. after it's dry use marking pen to decorate (eyes, ect).
my mom took a powder free glove (medical type) filled with water, froze, break off the glove and float your icy hand in the punch.
but some of the best (and cheap) ideas i've seen are at
familyfun.com
enjoy your party!!!