Prepare the cake in a 13 x 9-inch cake pan per the package directions using the amounts called for of eggs, oil and water. (May use milk or buttermilk in place of the water)
Meanwhile, in a large mixing bowl whip together both banana and vanilla instant puddings with milk or half and half until thickened.
Remove the cake from the oven. Using the back of a wooden spoon or similar immediately poke holes all over the cake.
Spread the prepared pudding on top and into the holes. Cool completely.
Once cooled, layer banana slices over the pudding and frost with whipped topping.
Sprinkle the top with crushed vanilla wafers. Chill until serving.
May garnish each piece with one vanilla wafer, if desired.