Make and bake cake according to package directions in a 9x13-inch pan sprayed and line with parchment paper and spray it.Poke holes all over cake with a chop stick and fork tines as soon as it comes out of the oven. Set aside to cool.
Place pineapple with juice in a medium saucepan and add sugar. Heat over medium heat for 10 minutes, until sugar is dissolved, remove from heat. Mix in the rum then pour evenly over the whole cake. Let cool to room temperature.
3Mix puddings and milk together until blended set aside to thicken slightly. Spread evenly over pineapple. Thinly slice bananas over pudding. Cover cake pan with plastic wrap and chill overnight or longer-- so cake absorbs syrup and moistens cake.
Mix the powdered sugar into the whipped topping and stir in the vanilla. Spread evenly over bananas; top with chopped nuts and toasted coconut if desired.