Right from the carnival site "What should I pack?
The first thing to remember is that you're on vacation and you are aboard one of our "Fun Ships" to have a good time. The second thing to remember is to travel light. If you keep those two things in mind, you should do just fine.
Casual attire and resort wear is the order of the day both on board and in port. Shorts, slacks, sundresses, blouses, etc., are in line for women. Clothing for men is just as casual. You should bring a pair of rubber-soled sandals or sneakers to wear on deck and a pair of good walking shoes. You might also want to consider bringing along a sweater or jacket for cool evenings and inexpensive rain gear in case of a sudden shower. Women may want to bring along a hat or scarf. You'll have a chance to dress up on two nights during 7 day or longer cruises (one night on shorter cruises) for the Captain's Cocktail Party and the Gala Farewell Dinner. On the other evenings you can dress casually for dinner (no shorts or tank tops).
For those not wanting to dress up, the Lido Restaurants are open nightly and have a casual dress code. Formal Wear: tuxedo; suit and tie; sport coat, tie and slacks; evening gown; cocktail dress; pantsuit Casual Resort Wear: sport shirts and slacks; dresses; skirts; pantsuit; Capri pants NOTE: Shorts, t-shirts, tank tops and bathing attire are not permitted in the Dining Room during dinner.
I does not say NO JEANS anywhere!!