Two 15-ounce boxes chocolate cake mix plus required ingredients
Four 16-ounce containers store-bought vanilla frosting (8 cups)
Blue gel food coloring, for the frosting
2 cups white and blue candy-coated chocolates, such as M&M's
7 ounces sweetened shredded coconut
A coupler is a two-part plastic device that lets you swap out piping tips on one pastry bag.