The website https://www.foodsafety.gov/keep/charts/refridg_food.html provides a complete list of what foods can be kept and which should be discarded after the power has been out for more than four hours and the food has been held at a temperature higher than 40°F. You can lengthen the time before your food spoils by filling a cooler with ice (or snow, if that is the cause your power outage) to keep the foods that you need most frequently to minimize the number of times you have to open your refrigerator. If the temperature outside is lower than 40°F, store your food in a sealed container outside.