Hi cruisin05,
Just like iriscruiser, I learned to pack lighter after my first cruise.
On Carnival's 7 day cruises there are usually two formal evenings. Don't be intimidated by "formal evening." It means you just have to be prepared to dress up as nice as you would like for dinner. I've found that there are very few tuxedos, but many women opt to wear evening gowns. If you want to use the dining room on formal evenings, I suggest you bring something really nice so that you feel comfortable among the other dressed diners in the dining room. You can opt to dine on the Lido Deck which is far less formal. What ever you decide, don't sweat it.
Other than that, the ship will be like your second home. Everyone is about having a great time and being as comfortable as possible. They won't be paying too much attention to what you're wearing.
Don't forget the trusty duct tape for little emergencies that might occur. You'd be surprised at the number of uses duct tape has.
I've decided to take plenty of underwear, socks, and a few shirts. I try to get by with four pairs of pants, one pair of dress shoes, one pair of deck shoes, a pair of sneakers and several accessories. No one has ever challenged my fashion sense.
If you pack light it leaves room for souvenirs you might want to purchase.
Now if you're a fashion plate, then go for it. The cruise is for you too. You can show off all of your couture collection and be smashing on formal evenings, but be prepared to look for a lot of help when it comes to lugging your luggage around.
I try to make it with one suitcase and one carry-on.