Layer half of vanilla wafers in bottom of casserole and put half of the bananas over it. Prepare pudding with milk as instructed on box and pour half of it over the bananas. Spread half of Cool Whip over it. Then start again with a layer of the rest of the vanilla wafers, the bananas, the rest of the pudding and the rest of the Cool Whip. On top sprinkle some vanilla wafer-crumbs.