Ok, well, considering your party is tommorrow and you haven't planned a thing... I don't know if I can be of much assistance, but I'll try. An easy solution is to just have a bunch of munchies, music, beach balls, water balloons etc. You can also play games with the water balloons and beach balls. Also, for food, order a pizza with pineapples on it, it will go with the theme that you are already trying for. I would give you waaaay better ideas, but since you only have less than a day, those are my only suggestions. Sorry if they don't help.