Make the "sand" by crushing the Nilla Wafers with a potato masher or in a food processor.
With a mixer, combine the Cool Whip, cream cheese, pudding mix, milk, and vanilla.
Layer a fifth of the crumbs in the bottom of a large, clean sand pail. Top with a third of the pudding mixture, then a layer of crumbs. Continue layering, ending with crumbs.
Cover and refrigerate at least 30 minutes. Decorate with the candy shells.