Preheat oven to 350 degrees. Lightly butter a 9-by-13-inch baking pan. Cut a piece of parchment paper large enough to cover the bottom of the pan and to overhang the longer sides. Place the parchment in the pan, butter the parchment, and set aside. In a medium bowl, whisk together flour, baking powder, and salt; set aside.

In a medium bowl using a wooden spoon, beat butter and sugar until light and fluffy, about 2 minutes. Add eggs and vanilla; beat until well combined. Add the flour mixture to the butter mixture; mix just until combined. Fold in half of the marshmallows, chocolates, caramels, and toffee chips.

Using an offset spatula, spread the batter in the prepared pan. Scatter the remaining marshmallows, chocolates, caramels, and toffee chips over the surface of the batter. Bake until golden brown and a cake tester inserted into the center comes out almost clean, about 35 minutes. Transfer to a wire rack until completely cooled. Using the overhanging parchment paper, remove from pan. Place on a baking sheet, and chill in the refrigerator until set, about 30 minutes.

Remove from refrigerator, and peel off the parchment paper. Using a serrated knife, cut into 15 irregular-shaped bars. Stack bars vertically. Store in an airtight container for up to 1 week.