My sister had a few Halloween birthday parties, and my favorite game was always guess whats in the jar. Get some jars or tupperware and darken the sides. Or any opaque container will work. Then inside put items like pealed grapes/witches eyeballs. Damp spaghetti with tomato sauce for brains. I can't remember the other items, but I'm sure you could find more ideas online. We would either put them on a table and have everyone go down the line putting their hands in the jars to guess what it was, or passed it around the table. Either way it gets lots of laughs and shivers. And don't forget to keep the lights low and play creepy music (you can buy good CD's at halloween stores, with doors slamming, chains rattling, etc.) to add to the effect.