Make and bake cake according to package directions using a 13x9" pan. While it is still warm, poke holes in the top with the bottom of a wooden spoon. Pour can of sweetened milk evenly over cake then do the same with the caramel topping. Refridgerate for an hour or so. Spread Cool Whip on top of cake. Break candy bars into pieces and sprinkle the pieces on top of the cake. Cake is best when stored in the refridgerater.