The chances of having leftovers are very low, but just in case you need to store any, you can store them in your refrigerator. Put any leftover cake in an airtight container and put it in the fridge. It will stay good for up to 4 days. If you need to store it for far longer, you can put it in the freezer. It should be good for up to 6 months. Defrost the cake overnight in the fridge before serving it. That said, I am not a fan of defrosted cake so I would not suggest doing this.