Preheat the oven to 350°F (175°C). Grease and flour a 9×13 inch baking pan.
In a large bowl, combine the yellow cake mix, 1 cup water, vegetable oil, and eggs. Beat with an electric mixer on medium speed for 2 minutes until smooth.
Pour the batter into the prepared baking pan and bake for 28 to 32 minutes or until a toothpick inserted in the center comes out clean.
Remove the cake from the oven and allow it to cool completely in the pan on a wire rack.
While the cake bakes, prepare the gelatin layers. Dissolve each package of gelatin separately in 2/3 cup boiling water (use 2 cups boiling water total, divided equally among the three gelatin packages). Stir each until completely dissolved and set aside to cool to room temperature.
Once the cake is cooled, use the handle of a wooden spoon or a fork to poke holes evenly all over the cake surface.
Pour the cooled strawberry gelatin evenly over one-third of the cake, spreading gently. Refrigerate for 10 minutes until slightly set.
Next, pour the pineapple gelatin over another one-third of the cake and refrigerate for another 10 minutes until slightly set.
Finally, pour the cherry gelatin over the remaining one-third of the cake and refrigerate for at least 2 hours until fully set.
Once the gelatin is set, spread the whipped topping evenly over the entire cake.
Arrange the sliced bananas evenly over the whipped topping.
Sprinkle the crushed pineapple, chopped maraschino cherries, and chopped walnuts evenly on top of the bananas.
Drizzle the vanilla extract over the top for added flavor.
Refrigerate the cake for at least 1 hour before serving to allow flavors to meld and the cake to chill.