Frost entire cake with remaining frosting. Cut licorice pieces to desired length for the mast; place near the edge of the longest sail. To create the top flag, spread a thin layer of frosting on a small piece of aluminum foil. Unroll and remove wrapper from fruit snack roll; press onto frosting-coated foil. Using kitchen scissors, cut into flag shape. Secure flag to mast with a small amount of frosting. Use candy for portholes, or decorate as desired. Store loosely covered.