kabobs - fruit ones and then meat/veggie ones.
In Hawaii they really like SPAM (the lunchmeat) so spam kabobs would be very Hawaiian
I love those beach cupcakes - that's really cute.
You could just do a cake that way; it would be faster.
Centerpiece: how about a little kid's beach chair (dollar store) with a beach towel, bucket, pail, lei draped over it, a coconut or two, suntan lotion, sunglasses, and a cute picture of your BF (boyfriend?)?
Punch is pretty easy: 2 or 3 liters of ginger ale (not Sprite or 7-Up) , same amount or a little less of pineapple juice, lime sherbet (if you can get, it pineapple sherbet).