The best ways to store leftovers using aluminum foil involve ensuring the food is cool before wrapping, covering the entire dish tightly, and sealing the foil properly. First, let the leftovers cool down to room temperature to prevent condensation. Then, wrap the dish completely with aluminum foil, making sure to cover the edges and corners to avoid air exposure. For added protection, you can double-wrap the dish. Seal the foil by pressing the edges together firmly. Store the wrapped leftovers in the refrigerator or freezer, depending on how soon you plan to consume them.