Will anyone else they know be there with them? If so, maybe someone can Skype the ceremony so you can watch it live with your family.
Arrange for a bottle of champagne and some glasses to be waiting for them in their honeymoon suite. Or fresh flowers for the room. Or leis to wear.
Send a collection of iTunes of classical wedding music often played during ceremonies via e-mail to enjoy the music long after the wedding.
Send them a gift certificate for a meal at a nice restaurant or for a picnic lunch they can take to the beach.
Bathing suits and sunscreen? Sunglasses? Nice beach towels?
We got married on the beach on Lake Michigan. We provided sun umbrellas to our guests--they may need them as well depending on the time of day of the ceremony.
Myself, I'd hide in luggage and go. :)