Cool leftover waffles on a rack and seal them in a food-storage bag. Refrigerate or freeze within 2 hours of cooking, or within 1 hour if the temperature is above 32°C (90°F). Refrigerate at 4°C (40°F) or below and eat the next day, or freeze at −18°C (0°F) for up to 2 months for best quality. Thaw overnight in the refrigerator, then reheat in a preheated waffle iron until hot throughout. Start checking after about 1 minute to avoid overbrowning.