Bake the cake as directed on the box.
Cool completely.
Once cool, use the straw to poke holes all over the cake, making sure to go all the way to the bottom of the pan.
Pour the condensed milk over the cake, filling the holes.
Repeat with the caramel topping.
Spread whipped topping over the top of the cake.
Sprinkle toffee chips over whipped topping.
Chill before serving.