I would make it so I could shit money.
I would be curious to see how you manage serial numbers and technically making what is illegal currency, not to mention if one of those bullion coins decided to come out sideways...
It would probably be better to be able to make or purify some hard to come by substance. There are bacteria that refine gold these days so having a quite literal Midas touch would be an option, though there are better ones than that; http://www.scientificamerican.com/article/strange-but-true-whale-waste-is-valuable/