Ensure that the cranberry juice, pineapple juice, and ginger ale have been in the refrigerator for at least 4 hours. Using cold ingredients prevents the ice from melting too quickly and diluting the flavor of the punch.
In a large punch bowl or a 1-gallon pitcher, pour in the 4 cups of cranberry juice and the 2 cups of pineapple juice. Stir them together gently with a long-handled spoon until the colors are well blended.
Just before you are ready to serve, slowly pour the liter of ginger ale into the juice mixture. Stir very gently once or twice to combine. Avoid over-stirring, as you want to preserve as many bubbles as possible for that festive fizz.
Float the fresh cranberries and orange slices on top of the punch. Add ice cubes to individual glasses rather than the bowl to prevent dilution, or add a large ice ring to the bowl. Tuck a few rosemary sprigs into the bowl for a pop of green and a subtle holiday aroma.