I agree with most of the posters on this board about wearing the tux...here's another thing I can offer since I just got back from the Explorer of the Seas (Royal Caribbean as well).... ship photographers will be taking pictures all over the place throughout your cruise and will make those photos available near the end of the cruise trip... since this is your first cruise (?) you probably want some sort of memory that you had that "james bond" look.... on your first formal night which you will find out, many make a big deal about.

An alternative, would be to wear a dark suit but get a pair of snazzy shoes, a tie and a "vest" which would help set off the look of the suit from just looking like any other person in a suit....to save weight (if you like) you could use the same suit, just drop the vest and change the tie and shirt for the 2nd formal night and nobody will be the wiser.......hope this helps cover your 2 formal nights

Now....on to daily wear.....

Wear anything comfortable to walk in such as jeans (1-2 pairs), casual pants (2-3 pairs), and shorts (2-3 pairs). Shoes are descretionary to each person so I'll just tell you what I took and you can use it as a guideline.....

1 pair tennis shoes
1 pair dress shoes
1 pair sandals
1 pair flip flops for the beach excursions

The most important part with the pants/shorts/jeans is to be able to wear the pants again but with different shirts so this also can help save some weight on your luggage. The shirts I mostly saw were the hawaiian type shirts or your casual shirts with collars and of course t-shirts for people just hanging out near the pool or sunning on the deck.....

let me know if you need any additional information and/or tips and I'll be more than happy to answer...