Bake cake as directed on box in greased and floured 9 x 13 inch pan. Heat pineapple and sugar until sugar is dissolved. Punch holes in cake while still hot and pour pineapple-sugar mixture over cake. Refrigerate until cool. Mix pudding as directed on package and spread over cake. If using coconut, sprinkle some on cake at this point. Mix rest of coconut with Cool Whip and spread on cake. Cake must be kept refrigerated.