To check into the hotel, only your name and photo ID (I think). You will check in at the couples station at the airport. They will let the acutal hotel kknow that you coming. You will need your passport and photo ID for the airport. If you sign up for the couples reward you can register your airline information and that helps couples to schedule your travel back to the airport.
Personally I always take the email confirmation just case you have any problems, but it is not required.
We had a booklet from out travel agent that we gave them. Also a photo ID and a credit card. They put a $300 hold on it for room incidentals. You can pay your room charges in cash when you leave and they will put the $300 back on your card, but it is something you should know before going. Couples does mention this on their site but a lot of people overlook it. The resort is "cashless" so anything you buy extra like at the spa or gift shops will be charged to your room. This is why they do this.