Refrigerate Halloween Party Food Meatballs within 2 hours of serving and keep them in a shallow airtight container for up to 4 days. For freezing, cool the sauced meatballs completely and pack them without the mozzarella eyes. Freeze for up to 2 months, then thaw overnight in the refrigerator. Reheat the meatballs covered at 350°F for 15 to 20 minutes or until the centers reach 165°F. Add 2 tablespoons of marinara if the sauce looks thick, then make fresh cheese eyes. Discard leftovers if they smell sour, feel slimy or show mold.