Having just returned from a RCI cruise we found a couple of ways to get yourself a nice smoothie or milk shake for free.
Most evenings there was a cold soup on offer such as strawberry and mint. Many people pass these over but if you take one and put it into a glass it makes a superb drink.
Fancy a milkshake, grab a glass and first fill it from the soft ice cream machine, then top up the glass with coffee or hot water and stir, just like the MacDonalds thick shakes. You can make a few combinations depending which ice cream you use, try the mixed chocolate and vanilla with hot coffee for a mochachino, choclate ice cream and water for chocolate shake and vanilla and water for a vanilla shake.