Super capacitors are awesome, cheap, easily obtainable and can be a little dangerous. They have a massive energy density and are willing to give up their energy very VERY quickly.

You don't have to discharge all this energy all at once, as fun as sublimating copper and throwing sparks is, they can be discharged at any rate, meaning you could connect it up to an LED to power it forever more, or for example a Pi for a good while.

So I gave it a go and it worked!