I used three boxes of cake mix for this treasure chest cake; one for lid, and one for each of the two layers on the bottom. (I used pans that were about 14×10.5 for each of the three layers.) I used a very thick chocolate buttercream icing. On the lid, I put a LOT of icing in the center (longwise) and domed it to have a curved lid (it’s not the cake that’s curved).
The metal strips and rivets are fondant, painted with the silver and copper powders (mixed with a drop of a clear-colored extract) found in the cake decorating isle. The treasure map is fondant, painted, slit edges, and rolled at top. Sand is brown sugar. Gold nuggets are gold nonpareils. Coins and gold bars are from Cost Plus, some of them are glued into place with a smidge of icing.
The lid cake is on a foil covered piece of cake cardboard, cut to size. It is held up by five wooden dowels cut to size; two longer ones up front to keep lid open – hidden by coins, and three at the very back, cut shorter. Put hole/notches in the bottom of the lid cardboard, where the dowels will rest in so the lid doesn’t slip off. It is a bit tricky getting the lid on just right, it took two of us to do it! Oh, I cooked the cakes a little longer to make them more dense so that the treasure chest would hold up. The whole thing is on a wooden cutting board covered in foil.