This is a fun game and easy! Let's set up a trading post, an Herb Shoppe, where we can trade herbs for all those wonderful conconctions we need to mix up for all sorts of things. Actually, we can use any plants or plant parts or tree parts for our magic purposes.
I will begin by trading:
Comfrey for Rosemary for my liniment.
Now, you trade the Rosemary for.....? and tell us why you need the new herb.