Spices
The original use for spices was to take out the funky flavor from spoiled food. As you remember, Columbus sailed in search of a shortcut to these spice which were considered a treasure on par with gold and jewels. Common sense will dictate how to stew, boil, or overcook foods to a safe level. Spices and salt will make this still nourishing food edible. Of course spices will be a valuable barter item if international trade is stopped.
Charcoal Medicine
Charcoal is a great first line treatment for loose stools. For example, a slice of bread burned over flame until there is just a little gray ash can be consumed along with copious amounts of water to wash it down, this dose works for most non invasive diarrheas. Diarrhea was formerly a major killer. An improvised treatment could save your life from dehydration and electrolyte imbalance.