Pastry bags are commonly used for adding the finishing touches on frosted cakes, however you can use a pastry bag for piping any kind of semi-solid food. Pastry bags can never be in short supply, especially when you consider that decorating a cake with 3 or 4 different colors requires just as many pastry bags cleaned and ready to go. Stock your kitchen with several pastry bags so you always have something clean and ready to go!