So, about the cruise mates and how it works:
We would find a travel agent, we can use one that you know of or one that I know of, or we may even be able to book directly through carnival. But from what I understand, Travel Agents are sometimes cheaper. So once we agree who to use to book our cruise, we would each give them a call and book our portion of the cruise, and separately give our credit card info. Then, at check in we would each have our own sail n sign accounts. If you're not familiar with the sail n sign account I'll explain it: When you're at the port checking in, you give the person checking you in either cash or your credit card, and they give you a card which you use throughout the ship. It's used as your id, you can use it to buy things, buy drinks, gamble, buy excursions. It's an all in one card. You and I would each have our own card and we wouldn't have access to each others cards.
The lady I just recently booked a cruise with here on cruise mates suggested this to me for personal valuables like money, passport, jewelry: We can each have our own little safety envelope (which they sell at walmart, like a money envelope with a lock on it) and then we would be able to store both of our things in the in-room safe.
Easy as that!!