From what I can tell they are coupons that can be used towards the cost of various services, a romantic beach dinner for two, Zentropia SPA treatments, car rental or excursion, and more!
I have read that as an example you get:
(2) $30 credits toward “Hotelextras excursions”. One credit can be used per excursion..
(2) $10 credits towards the segway tour, (1) $30 credit toward a minimum 2-day car rental, and (1) $30 credit toward scuba diving and others such as a coupon towards an upgrade ect.
Although this is a nice “extra” and you may find some of these useful when visiting; I would not book just for this. I would imagine based on my past experience with this sort of deal from other hotels there will be many limits and restrictions.