Prepare the cake mix in a 9x13, according to the package directions.
As soon as the cake is finished baking, poke holes all over it with a fork. Whisk together sweetened condensed milk & caramel ice cream topping. Pour it over the hot cake. Chill for 2 hours in refrigerator.
When chilled, spread Cool Whip over the cake. Sprinkle candy bar pieces over top.