Bake cake according to package directions for a 9x13 inch pan; cool on wire rack for 5 minutes. Make slits across the top of the cake, 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; then sprinkle the snicker bars liberally across the entire cake while still warm. (Hint: I chop my candybars into small chunks as opposed to crumbs - I like to have pieces I can chew on!)
Let cake cool completely, then top with whipped topping. Decorate the top of the cake with some more candybar chunks and swirls of caramel topping. Refrigerate and serve right from the pan!