Prepare and bake cake according to package directions for a 9x13 cake. Remove to cake plate and cool completely. Meanwhile, chill a large metal mixing bowl and mixing beaters. Combine chilled whipping cream and powdered sugar in chilled bowl. Beat with electric mixer at high speed until stiff peaks form. To test, lift beaters from whipped cream - stiff peaks should remain on surface. refrigerate until ready to use.
When cake is cooled completely, frost with whipped cream. To decorate, pipe whipped cream along the top edge of the cake and along the bottom edge. Sprinkle the chopped candy bars in a rectangle on top of the cake, just within the piped edge, leaving an empty rectangle in the center. Sprinkle the chopped peanuts in the center rectangle. Put the ice cream toppings, separately, in two zipper sandwich bags. Cut the corner tip off of one of the bags and drizzle the ice cream topping in a zig-zag pattern across the whole cake diagnally (it's Ok if some gets on the piped edge). Repeat with the other bag and drizzle in the opposite direction.