I've never had mine searched by the cruiseline, only at the airport. I usually have a lock on my luggage so that way I know if they've been in it or not. From what I've heard they really don't give you a hard time about bringing some beer, wine or soda on board.
I take soda on board everytime I've cruised with no problems. I have seen them "hold" wine/liquour that folks brought on board until the end of the cruise for them, however just as many times I've seen folks carry it right on board. This is a policy that seems to change quite a bit. You may want to read the FAQ at http://www.royalcaribbean.com. For the most part, if you keep it in a small duffle bag and just walk on with it you'll probably be allowed to take it on board.
I recently sailed on the ROS I took two bottles of wine in my checked bags. I packed them carefully in the event they broke. I found them to arrive perfectly in my cabin. I also saw people carry on 12packs of Dr Pepper. Enjoy your trip! Due to Hurricane Claudette our intineary changed.
I don't know about soda but the liquor policy is that if you buy on the islands, they hold until you get back and deliver to your room. They have a soda card you can buy on board that gives you unlimited sodas but I think it is only for kids. Don't think they will search your bags but is it worth the risk of getting soda on everything? Soda is included with meals in the dining room by the way.
Interesting... just looking for some info on RCCL site and they say that fountain drinks are 1.50 with free refills in dining room. I have never know this to be the case. Don't know if this is new or if the wait staff just ignores it. ANyone know? I will post a new thread for it.