Each person will have their own Folio number - so you will be 001 and your mate will be 002. So when you get your final bill it will be really easy to spot what 001 has paid for and what 002 did. Here is link to prices for froo-froo drinks http://travel.webshots.com/album/559018541CiiBCu?vhost=travel.
You can also register a credit card for each person, irrespective of how many are in the cabin, either using the online check in (that's what we as a family do), OR you can do it at the desk prior to embarkation, (takes longer). You will then each receive a separate folio on the last night & individual names & account totals will appear on your 'on screen' account on your cabin TV throughout the cruise.