Preheat oven to 350 degrees F. Grease and flour two 9x9x2-inch baking pans; set aside.
In a large bowl, beat together the cake mix, pumpkin, cooking oil, brown sugar, 1/4 cup water, cinnamon, allspice, and nutmeg on medium speed 1 minute or until just combined. Add eggs, one at a time, beating well after each addition.
Divide batter evenly between prepared pans. Bake 30 to 35 minutes or until wooden toothpicks inserted near the centers of cakes come out clean. Cool cakes in pans on wire racks for 10 minutes. Remove cakes from the pans; cool completely.
Wrap and freeze cakes at least 2 hours or until partially frozen. Level cake layers by slicing off the rounded top part of each cake with a long serrated knife. Cut each cake layer vertically into four squares.
Tint frosting with paste food coloring, creating equal amounts of two colors. Spread about 1/4 cup frosting over top of one of the cake squares. Place another cake square on top and frost. Repeat with two more cake squares, forming a tall, rectangular bag shape.
Secure by inserting four 4-inch wooden picks vertically down through the cake layers near the four corners. Repeat again with remaining 4 cake squares and frosting.
Frost tops and sides of the two tall cakes. If desired, use decorator icing to write on and/or decorate sides of cakes. Add large and small Halloween lollipops and candies, and if desired, tinted coconut, making 2 cakes. Remove wooden picks before serving.