As long as milk is consumed within a few days of the date printed on its container, nothing will happen; milk is generally safe for consumption for a few days past this date, according to the Dairy Council of California. Most brands stamp the sell-by date on milk containers, not the use-by date or expiration date, and as long as the milk inside smells good, it is safe to drink it and cook with it. Milk that isn't used before spoiling can be frozen and used later on in recipes, oatmeal, pudding and soup.
Extending the freshness of milk requires storing it at the proper temperature inside the refrigerator. The interior temperature for proper milk storage should be 38 to 40 degrees Fahrenheit. Milk should be brought home from the store quickly and put in the refrigerator right away. It shouldn't be left out on the counter or table after serving, as this can allow for bacteria to grow inside the milk and hasten its spoilage.
When purchasing milk in the store, pay attention to the sell-by date, making sure that it is a date in the future. Plan ahead to ensure that the milk will be used up before that time.