The Liver Flush stimulates the digestive system. You'd quieted yours down during the Master Cleanse, so this stimulation is more noticeable.
Be ravenous, but focus on eating mostly healthy foods or you're going to gunk up your cleansed guts. The focus on junk food is a mind craving. Substitute healthful alternatives with some similarity to the food you crave.
Ice Cream? Could be that your body wants good fats to keep the bile flowing, so your liver doesn't re-clog.