Prepare cake mix as directed on box. Pour half of cake batter into greased 13 x 9 x 2 cake pan. Bake 15 minutes at 350 degrees.
While cake is baking, in a saucepan, combine caramels, milk, and butter. Cook over low heat, stirring until the caramels are melted. Remove from heat and set aside.
Remove cake from oven after 15 minutes and pour melted caramel mixture evenly on top of cake. Sprinkle the chocolate bits and nuts evenly on top of caramel mixture. Spoon remaining cake batter over the top. Bake 30 minutes at 350 degrees. Let the cake cool before cutting.