RIU Merangue???

Question

I am booked at the RIU Merangue for Feb 22/08 till Feb 29?08. I am wondering if they charge your credit card for anything upon check in or if you even need to present your credit card at checkin. I'm just curious becuase if they charge it for anything I'm wondering hom much I should have on it. also, how much money would be good to have on me? I dont plan to do any trips or anything and I'm not one for buying suvineres. any help would be great!