I have five 1622 3 polkers Sigismund III from medieval Poland. What could these purchase in medieval times? My searches only takes me to eBay and collector sites.
As an aside, 1622 is Early Modern rather than medieval era.
Now, regarding the question: not very much. The value of these coins is 7,5 grosz, which around that time was about a daily wage for an unskilled laborer, maybe slightly less.
That could get you a chicken OR 2 pints of beer OR a pint of mead. These are prices from around 1640 btw, you might buy a bit more in the 1620s.
Not much more though: around 1626-1629 a horse could cost 1500 grosz, a hat 14, a sheepskin coat 150, shoes 53.