If you have Blueberry Brew, Elderberry Elixir, or Woad Wine, you can exchange it for a Milk of Human Kindness in the second row from the bottom third square from the left. It won't hurt to have that, especially if you haven't fought Macbeth yet. But be careful; some muggers are keeping an eye on people who walk away with the Milk and you might find yourself having to fight off dairy addicts.