A magic spice jar could produce whatever spice—rare or otherwise—that the possessor wanted. If that spice were not used within a few seconds, it would fade from existence. If it were added to food or drink, however, it would magically change the food or drink in addition to seasoning it. Food or drink seasoned with the spices from the jar would be purified of any contaminants, disease, poison, or filth. Up to a dozen people eating or drinking something seasoned with the magic spice would also find their health restored by a small amount. Moreover, they would be resistant to most diseases for the next four hours.
A spice jar could produce enough spice to season three meals worth of food and beverages for twelve people per day. The magic would only affect the same person once per day. Other than these limitations, the jar would never run out.