Try our freeze-ahead Slushy Red Roosters, and ask a guest to tend the blender.
Stir together cranberry juice cocktail, orange juice concentrate, vodka, and 4 1/2 cups water. Place 1 (1-gal.) zip-top plastic freezer bag inside another 1-gal. zip-top plastic freezer bag. Pour about 4 cups cranberry mixture into inside bag. Seal both bags. Repeat procedure with remaining cranberry mixture. (Double bagging is a precaution to avoid spills.) Freeze bags 24 hours. Remove bags from freezer; let stand 5 minutes. Process cranberry mixture, 1 bag at a time, in a blender or food processor until desired consistency. Pour into glasses. Serve immediately.