Mix together cake mix, melted butter and 1/3 cup evaporated milk. Press 1/2 of mix into a 9 x 13-in. greased pan. Bake at 350 degrees for 6 minutes. Remove brownies from oven and sprinkle on half the bag of Heath toffee bits. Melt together caramels and rest of the evaporated milk, pour over toffee bits. Sprinkle on half the bag of chocolate chips. Spread the remaining batter on top (this is easiest if you take pieces of the batter, flatten each individual piece in your hands and place on top). Sprinkle remaining toffee bits and chocolate chips on top. Bake at 350 degrees for 20 minutes. Refrigerate for 3 hours before serving.