- Preheat the oven to 350°F. Spray a 9x13-inch baking pan with nonstick spray and set aside. 
- Prepare the cake mix according to box instructions. Pour the batter into the prepared pan and bake according to the package directions. Allow to cool for 10 minutes. - 15.25 ounces box yellow cake mix, 1 cup water, ½ cup vegetable oil, 3 large eggs 
- While the cake is cooling, make the pudding. In a small bowl, whisk together pudding packets and milk until thickened. - 6.8 ounces instant vanilla pudding mix, 3 cups milk 
- Using the end of a wooden spoon, poke holes all over the cake. Spread pudding mixture on top and top, then layer with ⅔ of the banana slices. Cover with plastic wrap and refrigerate at least 30 minutes. - 3 bananas 
- Spread whipped cream on top, then garnish with the remaining bananas and sprinkle all over with vanilla wafers. - 16 ounces Cool Whip, 20 vanilla wafer cookies