In a large bowl, combine the cake and pudding mixes, water, oil, eggs and extract. Beat on low speed for 1 minute or until moistened; beat on medium for 4 minutes.
Line a 13x9-in. baking pan with waxed paper; grease and flour paper. Pour batter into prepared pan. Bake at 350° for 30-35 minutes or until a toothpick inserted in the center comes out clean. Cool for 10 minutes before removing from pan to a wire rack to cool completely. Frost.
Editor's Note: Banana extract is available at cake decorating and candy supply stores.