KEEP THE FREEZER DOOR CLOSED. Keep what cold air you have inside. Don't open the door any more than necessary. You'll be relieved to know that a full freezer will stay at freezing temperatures about 2 days; a half-full freezer about 1 day. If your freezer is not full, group packages so they form an "igloo" to protect each other. Place them to one side or on a tray so that if they begin thawing, their juices won't get on other food. And, if you think power will be out for several days, try to find some dry ice. Although dry ice can be used in the refrigerator, block ice is better. You can put it in the refrigerator's freezer unit along with your refrigerated perishables such as meat, poultry, and dairy items.
EVEN IF FOOD HAS STARTED TO THAW, SOME FOODS CAN BE SAFELY KEPT. The foods in your freezer that partially or completely thaw before power is restored may be safely refrozen if they still contain ice crystals or are 40 F or below. You will have to evaluate each item separately. Generally, be very careful with meat and poultry products or any food containing milk, cream, sour cream, or soft cheese. When in doubt, throw them out.
In general, refrigerated items should be safe as long as power is out no more than 4 hours. Keep the door closed as much as possible. Discard any perishable foods (such as meat, poultry, fish, eggs, and leftovers) that have been above 40 F for 2 hours or more, and any food that has an unusual odor, color, or texture, or feels warm to the touch.
KEEP AN APPLIANCE THERMOMETER IN THE REFRIGERATOR AND FREEZER AT ALL TIMES. This will remove the guesswork of just how cold the unit is because it will give you the exact temperature. The key to determining the safety of foods in the refrigerator and freezer is knowing how cold they are. The refrigerator temperature should be 40 F or below; the freezer, 0 F or lower.
More detailed information, along with a chart that tells which foods may be saved and which should be thrown out, may be found in Keeping Food Safe During an Emergency.