I have heard some cruise lines do not allow onboard walkie talkie use, so best to check. But many do sell the bubblepack FRS/GMRS radios in their gift shops. Legally, unlicensed people should stick to the Family Radio Service channels (channels 1-14) but I doubt one out of a hundred people even realize that the other channels require a license.

But if you get dumped in some foreign port, I would hesitate to use the radio (actually, it would be illegal in most cases) because those frequencies could be allocated to, for example, police or military use in other countries. Wouldn't want to annoy those folks with radio chatter about how you're running out of diapers.

Depending on how many other passengers or crew are using similar radios, the airwaves could be so busy that they are basically unusable in some incident, so plan accordingly. At least pick a meeting point--maybe one near your assigned lifeboat in case of evacuation, and for all other situations that prevent you from going back to your particular cabin, pick another meeting place someplace comfortable, like your favorite bar, or the cabin of friends, fi they are away from yours.