Answer: If we are talking about a standard sightseeing cruise, there is no specific dress code and you can wear whatever is comfortable for you. Still, it is a good idea to wear comfortable shoes, and if you plan to spend time on the outdoor deck, consider bringing something warm in case it gets chilly from the wind.   

If you are planning to take a dinner cruise, some companies do request a certain type of dress code. That does not mean you need to show up in a tuxedo or an evening gown, but you will usually be asked to dress in semi-formal or smart casual attire. Be sure to check with the specific cruise company you are booking with to know what is expected.