It also depends on which restaurant you intend to visit for the occasion - some will do a cake for you. For example, I called Ohana in advance last November and they made a birthday cake for my brother for our December visit. Yachtsman Steakhouse didn't have the kind of cake I wanted, so I ordered from the Boardwalk Bakery for my parents anniversary, picked it up, and carried it to the YS. Disney Dining can tell you which of the restaurants can provide you with a cake.