Don't worry yourself over the little details or you won't be able to enjoy the anticipation of your first cruise! You have definitely come to the right place for advice!
The most important thing I can suggest is that you bring a printout of your embarkation form. This was actually advice I got from an RCCL Cust. svce. rep. He said, "Sometimes 'things happen' to computer records and the last thing you want is a problem with getting on the ship."
You are only going for 4 nights. I believe that means one formal night and two casual nights. Pack a nice dress and a pair of neutral slacks or skirts and two nice tops. Done.
Pack some comfortable shorts and shirts for during the day. Don't forget to pack a light sweater because sometimes the ocean breeze can be a bit cool for some people.
Pack some Bonine just in case. I just feel better knowing that it's in my case even though I don't use it.
Sunscreen and extra sunscreen. We also found that walkie-talkies were nice because occasionally my husband and I like do do things separately (that happens after many years
). I also pack a few bottles of water to bring with me.
Don't sweat the small stuff. Pack clothing and necessities and I know you will have a good time!