Leftover Spaghetti and Meatballs can be stored in the fridge for 3 to 4 days. They can also be frozen for up to 3 months for best quality. Make sure that you allow it to cool down, then place it in an airtight container. If freezing, it's best to store the leftovers as flat as possible. A vacuum-sealed bag is perfect for this. Defrost in the fridge overnight or in a bowl of cold water that is changed regularly. Reheat in a saucepan over medium heat until warmed through.