Decorate the Jack-O-Lantern: Bring a real pumpkin, with some squares of Velcro in the spot of the eyes, nose, and mouth. Make face parts out of felt or foam (samples HERE and HERE). Have songs written on each part and let the kids take turns picking songs and decorating the pumpkin.
All images from: http://www.chicaandjo.com/2009/10/15/mix-and-match-jack-o-lantern-faces/
Our previous chorister used this Melissa & Doug Monster Puppet toy (I happen to have the same one) and named him Marvin the Musical Monster. The kids loved decorating him.