Preheat the oven to 350°F and lightly coat a 9x13-inch baking pan with non-stick spray.
Prepare the cake batter as directed on the package and pour it into the prepared baking pan.
Bake according to the cake mix instructions. Once a toothpick inserted in the center comes out clean, remove from the oven.
While still hot, use the handle of a wooden spoon or a chopstick to poke holes evenly across the cake.
Pour the sweetened condensed milk over the cake, allowing it to soak into the holes. Repeat with the caramel sauce.
Let the cake cool completely to absorb the liquids.
Once cooled, spread the Cool Whip evenly over the top.
Sprinkle Heath Bar bits over the Cool Whip layer, using as much or as little as desired.
Slice and serve immediately.