1 package (8 ounces) cream cheese, at room temperature
Preheat the oven to 350 degrees F. Lightly mist a 13- by 9-inch baking pan with vegetable oil spray. Set the pan aside.
Place the cake mix, water, oil, and eggs in a large mixing bowl. Blend with an electric mixer on low speed for 1 minute. Stop the machine and scrape down the sides of the bowl with a rubber spatula. Increase the mixer speed to medium and beat 2 minutes more, scraping the sides down again if needed. The batter should look thick and well blended. Pour the batter into the prepared pan, smoothing out the top with the rubber spatula. Place the pan in the oven.
Bake the cake until it springs back when lightly pressed with your finger and just starts to pull away from the sides of the pan, 35 to 38 minutes. Remove the pan from the oven and place it on a wire rack. Immediately poke holes in the top of the cake with a drinking straw or chopstick.
Prepare the topping. Place the caramel topping and sweetened condensed milk in a small bowl and stir to combine. Spoon this mixture over the warm cake so that it can seep down into the holes.
Measure out half of the crushed candy bars and sprinkle the pieces over the cake.
Place the whipped topping and cream cheese in a large mixing bowl and blend with an electric mixer on low speed until smooth and combined, 1 minute. Spread the mixture over the top of the candy.
Sprinkle the remaining candy pieces on top.
Place the pan, uncovered, in the refrigerator to chill the cake for about 20 minutes before cutting it into squares and serving.
Store this cake, covered in waxed paper, in the refrigerator for up to 1 week