When I was younger I used to perform a signed bill to lemon effect in most of my performances. I would have the bill signed, placed into an envelope, burned, then found in impossible location.
It honestly made no sense in the context of my act (I was young), but the reactions were always on point. For something like this, I think that effect would go over VERY well in the context of your performance. Could easily do it with a whole basket of fruit - oranges, lemons, limes, etc - and start the presentation by talking about the different nutrition choices someone can make with a single $20 bill - and then go into the effect.