Bake cake according to package directions for a 9×13 inch pan; cool on wire rack for 5 minutes. Make slits across the top of the cake or use the non-spoon end of a wooden spoon to make holes, making sure not to go through to the bottom.
In a saucepan over low heat, combine sweetened condensed milk and caramel topping, stirring until smooth and blended. Slowly pour the warm topping mixture over the top of the warm cake, letting it sink into the slits or holes. Then pour hot fudge, and finally (for now) sprinkle the crushed chocolate toffee or peanut butter bars liberally across the entire cake while still warm. Let cake cool completely.
Then top with whipped topping. Decorate the top of the cake with some more chocolate toffee or peanut butter bar chunks and swirls of caramel topping or chocolate or even both. Refrigerate and serve right from the pan!