Keep it cold.

For each 18-degree increase in temperature, the spoilage rate of milk doubles. If it takes 45 minutes to get milk from the dairy case to your home, milk may already have reached 60 degrees on a warm spring or summer day, so buy an inexpensive (and eco-friendly) reusable insulated bag or use a small cooler and ice pack for your milk's trip home. If stored properly, milk will keep up to five days beyond the sell-by date.