You can make your own piggy bank or buy a plastic one from the store. You can also use another type of animals like a penguin or duck (anything works). It take a little bit of electronic knowledge to make but is pretty simple.
Step 1: Building the piggy bank
Next you put plaster clothes dipped in warm water over the frame and let each layer dry for about 10 minutes.
Once you have a sufficient amount you sand down the layers to make it as smooth as possible (note: it will never be totally smooth unless you take a really long time and prep the wire frame better).
Let it sit overnight to allow it to totally dry.
Step 2: Create the "Guts"
Using a solderless breadboard,* wires, Two LED's, one resister that is at least 180ohm, and a 9 volt battery connect them according to the badly drawn diagram and picture.
The important part is to not connect the positive wire coming off of the 9V battery directly to the positive side of the breadboard, but, instead to insert the wire with a stripped end into one side of the penny box.
Insert another wire from the other side of the penny box into the positive side of the breadboard. This will allow you to connect the positive current when the pennies touch together inside the box. In a way it is like you cut the positive wire in half and are using the pennies to bridge the gap.
Make sure to use plenty of wires to leave room to stretch the parts out.