Spray a baking tray with cooking spray, then line it with a piece of parchment that extends past the sides. These will be the handles to lift out the dessert.
Visually dividing the pan into 8 equal rectangles, shape the chocolate chip cookie dough into a flat, even, rectangular shape that fits the divided section in the top left corner, making sure the edges are as straight and sharp as possible.
Shape the m&m cookie dough into a similar rectangle in the section diagonally across from the chocolate chip cookie dough.
Break the graham cracker sheets along their seams into pieces that are just as long as the cookie dough rectangles. Press them to form a wall in the bottom left section.
Place 2 full graham cracker sheets in bottom of the section.
Layer the chocolate evenly on top.
Spread the marshmallows across the chocolate.
In the section directly to the right of the chocolate chip cookie dough, carefully spread the brownie batter into a similar rectangular shape.
Roll two of the pie crusts together with about a 3-inch (8 cm) overlap, then trim it into a rectangle.
Preheat oven to 300°F (150°C).
On the far right side of the pan, lay the rectangular sheet of pie crust over where the 2 rightmost sections would be. Press the pie crust into the edges of the pan, then trim off any excess that goes beyond the pan.
Place a double layer strip of pie crust in the middle, creasing the dough near the bottom into the pie crust that was laid down in order to help it stick and stay up.
Seal off the left exposed edge of the pie crust with another double strip of pie crust. You should now have 2 rectangles completely enclosed in pie crust.
If the brownie mix has spread a little bit, push it back into its original rectangular shape.
Add the apple pie filling to the bottom right square.
Add the pumpkin pie filling to the top right square.
Immediately spread the banana bread batter into the section between the brownie and the pie crust.
Breaking another graham cracker sheet into pieces, form another wall along the bottom of the banana bread rectangle and the right of the m&m cookie dough.
Lay down 2 more sheets of graham crackers inside that rectangle to form a base, then evenly spread the cheesecake batter on top.
Bake for 1 hour.
Cool completely, then slowly and carefully lift the entire dessert out using the parchment paper handles. Immediately transfer to a large cutting board.
Make 8 evenly-spaced slices vertically and 4 slices horizontally, creating bars that are have 1, 2, or 4 flavors.
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