Gummy worm ice cubes - infest drinks as they melt. Put the worms in an ice-cube tray, letting them stick out of the top and sprawl over the edges, and fill tray with water; Add cubes to a clear beverage, and watch as kids squirm with delight.
Halloween spider decoration super easy and inexpensive= crepe paper and balloon. I added a smaller balloon (same type- just less air in it) for a head. next year I'm gonna add a red X made from crepe paper on it's butt.