Spoon the chocolate and vanilla frosting into separate zip-top bags. Press out the excess air and seal the bags. Snip a small (1/8-inch) corner from the bags.
To make Frankenstein's neck bolts, use a toothpick to poke 2 small holes on either side of the cone about 1-1/2 inches down from the top. Break a thin pretzel stick in half and insert the cut end into each hole, allowing about 1/2 inch to stick out.
With the bag of chocolate frosting, pipe the hair (around the open edge of cone), mouth, and scars on the cone. Pipe 2 dots of vanilla frosting and add candies as the eyes.
Combine the pretzel sticks, salted peanuts, O's cereal, and crackers in a bowl. Carefully fill each cone with the snacks, allowing them to stick haphazardly out of the top of the cone. Makes 12 cones.