This may be more troublesome than it's worth, but I just throw it out in case it's interesting to any of the builders. I used to like making levels for Age of Empires 2 as much or more as playing them so that's the only reason I mention it. That was a lot lot simpler though.
A new plant and at least 3 new items could come about: Olives, olive oil, and whale oil.
Olives could be a new plant which produces raw olives, or olive oil if the recipe is followed or whatever.
The oil could give a bonus on skill checks for cooking perhaps, but the main idea is it could be used as lamp oil. So, it could replace the regular oil already sold in stores, at the same price.
Whale oil could be a new item, which is cheaper, but also gives characters an temporary affect of stinking of lamp oil. Olive oil burns much more cleanly, so wouldn't produce a smell.
IF I'm correct and an modern acre of olives produces around 400 pints of average olive oil, maybe it'd be fair to say an olive plant in game could produce 1 or two pint's worth of oil per in game month, since it's medieval era farming practices.
