Teeth. I would show off my teeth as a start to my entrepreneurial apothecary business. Our average dental hygiene is way way better than what they had then, and consequently our teeth look like divine pearls in comparison. Hopefully, their amazement will allow a perceived transference of my expertise to other medicinal areas.

Also, knowing more math might help me make coinage with some simple engraved code that needs to be combined with the name of the bearer in order to be verified (only feasible for inter-medieval banks). This would be impetus for trade across greater distances.