You can freeze this cake. Wrap the whole cake or individual slices tightly in a layer or two of plastic wrap, followed by a layer of aluminum foil. Freeze in a freezer bag or airtight container for up to 3 months. Thaw at room temperature for a few hours or overnight in the fridge. Rum cake slices are delicious toasted! Warm a slice in a skillet with butter or pop it in the toaster until golden brown.