Taking in extra liquids helps keep the sputum more fluid and therefore easier to expel. It doesn't really matter what type of liquid you drink, although tea, soup and other warm liquids may feel better than cold ones. As a bonus, warm fluids may also soothe the irritated throat that may result from all that coughing.
You can also use water for a steam treatment. Fill the sink with hot water, bend down to it, cover your head with a towel and breathe in the steam. Add a few drops of eucalyptus, peppermint or rosemary oil, if you have one of them. These help clear and soothe the respiratory passages.