Whisk together melted butter, sugar, and cocoa in a mixing bowl till smooth. Add eggs and vanilla and whisk till blended. Stir in flour and salt.
Spread batter in a 9x13" pan that has been lined with foil or parchment paper and sprayed with non-stick spray. Bake at 350 ° for 30-35 minutes or until a toothpick comes out clean.
Remove from oven and immediately sprinkle with chopped Hershey bars, graham cracker pieces, marshmallows, and chocolate chips.
Return to oven and broil for 2-3 minutes or till marshmallows are toasted and chocolate is melted.