Muumuus or formal wear?

I have never been on a cruise and I am at a loss as to what to wear.

Someone said to bring a nice dress for dinner. Do we have to dress up for this cruise? I thought it would be a shorts and flip-flop affair. Perhaps a lovely tropical muumuu or two. No matter what, I am not bringing any pantyhose. No way, no how.

Is business casual appropriate? Someone else mentioned wearing layers as the session room can be cold. Any ideas anyone?