The recent incidents of disabled cruise ships make me think that you'd need to be to pay particular attention to hygiene and infectious diseases: sanitizer, latex gloves, face mask, and antibiotics. (Of course, if you get a norovirus infection, there is no treatment for it.) A supply of plastic bags might be a good idea.

You might also want to bring some survival ration like Datrex. I don't think people starved in the recent incidents, but maybe the next one will be worse.

Some light source with a long battery life, and some spare batteries, would be necessary if there is a blackout. Carry it in a small bag, along with a map of the ship.

I think there are some threads discussing this issue, so you might want to look them up.

Caveat: I've never been on a cruise, so I have no idea what I'm talking about. But I do think I'm right in offering the following advice: be alert, but enjoy your trip! Take some pictures for us!