The past 3 years we have been on a cruiseship on Halloween. On the last one people really planned and dressed up. I had a dress made to be comfortable - floor length muumuu which was black from one direction and red from a different angle and had silver spider webs covering it - from the novelty fabric dept at Joanns.
I was the black widow. Bill felt he was dressed up because he wore a Blackwater shirt. Not dressed up - it was one of his old polo-type uniform shirts brom Baghdad with Blackwater and the Blackwater logo on it.
The two other cruise ships didn't do much for Halloween - a Halloween party and party and the staff was dressed up. But the last one people really dressed up! I'm just not willing to pack heavy for a cruise with things I will wear once although I did take the Black Widow dress.