It's well known that the Columbian Exchange greatly improved the variety and quality of food available to the average person in Europe, with the potato particularly having a large role. However, famines and mass death from hunger continued in the post Columbus era, even into 19th century.
While famine caused by war is impossible to fully stop (see Yemen today), there ought be a crop package that could insulate the medieval European peasant from hunger better than a potato or wheat monoculture. Is there anything that could work without being too vulnerable to a single strain of blight or a cold summer?