As with keeping meat fresh, milk, cream, and half-and-half should be refrigerated as soon as you get them home. If so, they will easily last a week past the official sell-by date stamped on the container. Remember, that date is just what it says it is — the last day you ought to buy the item at the store, not the last day you should consume it in your home.
That equation, however, is predicated upon the container being sealed until that date. In other words, milk purchased a week before the sell-by date and opened right away might not be as fresh as milk with a later sell-by date that is also opened as soon as you get it home. A good rule of thumb is: Use fresh milk within a week of purchase.
However, cultured milk products, like yogurt and sour cream, have a much longer refrigerated shelf life. This makes sense, since they are, in a way, milk that has been allowed to “spoil” under controlled conditions. As long as those products look okay (no orange, gray, or green fuzz anywhere) and smell reasonably fresh, they are good to go, no matter what date in on the container.
What about butter? Technically, it should be kept refrigerated; the USDA even recommends freezing butter that won’t be used within a few days. (The good news is that butter thaws easily with no change in flavor or texture.) Nevertheless, many people prefer their butter at a spreadable room temperature. If you too like your butter ready-to-go — that’s fine — just be sure to store it in a cool place in your kitchen and always keep it covered.
Home refrigerators, by the way, should be between 35°F and 40°F, although under 38°F is best. You can check the actual temperature of your fridge by leaving a simple glass thermometer inside it overnight. Once you have a reading you can adjust the dials and check again, repeating until you get the desired temperature.
Source: dailyrecipe, 4.17.2013