If you like beer, then your best bet is to buy it by the bucket. Take it to your room, and your room steward will keep your bucket filled with ice.
If one of you or both drink soda, then purchase a soda card. For a four day cruise it is 24.00. If you only drink one or two a day, then you would be wise to purchase indiviually.
Welcome to Cruisemates and welcome to cruising