These simple tips will keep your leftovers safe to enjoy, according to the US Department of Agriculture and the Centers for Disease Control & Prevention (CDC). 

• Be sure to place cooked food in the refrigerator or freezer within 2 hours of preparation or pick-up (in the case of take-out meals). Bacteria and harmful microorganisms grow most rapidly between 40°F and 140°F. If you leave food at room temperature for too long, the risk of food-borne illness is increased.
• Don’t keep leftovers longer than four days. After that, it’s time to discard them.
• Your refrigerator should be set no higher than 40°F to slow bacterial growth. Don’t rely on the built-in dial, since they’re not particularly accurate. Check the fridge temperature with a separate thermometer. The freezer should be cold enough to keep ice cream solid—0°F.
• Never defrost frozen food at room temperature. Instead, thaw it in the refrigerator or microwave. Another option is to set the food container in a bowl of cold water, changing the water every 30 minutes.