Giant cakes have a chance of spawning with one chest. The chest can contain any of the following:

Vanilla: Diamonds, Emeralds, Gold Ingots, Saddles, Name Tags, Leads,  Golden Apples, Cobwebs, Netherite Helmets, Diamond Chestplates, Diamond Leggings, Diamond Boots, Music Disc (Cat), Music Disc (Chirp), Music Disc (Stal), Bread, Netherite Ingots, Cake, Cookies,

HFE: Pea Shooters, Milk Chocolate Bar, Cheese, Peas, Chocolate Cake, Chocolate Doughnuts, Pink Doughnuts, Chocolate Pie, Pancakes, Candy Cane Blocks, Green Candy Cane Blocks, Jelly Blocks