Would you recommend booking excursions/activities in advance? We are going to Oahu and plan on swimming with dolphins, horseback riding, going to a luau, etc. Are these things you can generally book with the hotel/company when you arrive, or do they fill up quickly and need to be booked in advance? I'd really rather wait and see what our schedule/the weather looks like when we get to Oahu but also don't want to miss out.