@alisha-- Oils, spices, syrups like honey as well as vinegar and garlic are all natural preservatives. For olives, you could use salt, spices, oil or vinegar easily.
I think spices are some of the oldest food preservatives ever used. Spice was the main food preservative used to preserve and store meats and is still used to make traditional style sausages in many countries. I had the most delicious veal sausage in Germany that was preserved naturally with spices.