Preheat the oven to 350. Spray your 9 X 13 inch pan with baking spray.
Make cake as directed on cake box.
Remove cake from oven. While it is hot poke it with a fork all over the top. If you happen to tear the top up a little it is ok.
First pour sweetened condensed milk evenly over the warm cake. Then pour caramel sauce evenly over the top. It will soak into the cake. Let the cake completely cool. This can be done the night before (just refridgerate completely covered if you make this the night before).
Add the Whipped Topping. Spread evenly all over the cake.
Sprinkle the Heath Toffee Bits or the broken up candy bars all over the top.