Disclaimer: Although I have verified the legality of using license-free personal communications equipment in foreign countries, spectrum management regulations are subject to change or interpretation. When in doubt, always ask an authority in the host country you are visiting.
I have divided this section into three regions: East Caribbean, West Caribbean, and South Caribbean. The countries in which cruise ships make ports of call are listed in each section, with the frequencies or channels which can be used license-free in each.
The only frequency band which is universally authorized by the International Telecommunications Union (ITU) in Region 2 (the Americas, Caribbean, and some Eastern Pacific islands) is the 902-928 MHz band, and only when using digitally-modulated, frequency-hopping spread-spectrum walkie-talkies with no greater than one watt output power.
The PMR446 band is authorized in British and European countries, as noted. These frequencies are allocated in the United States for use by licensed radio amateurs. Therefore, if you were to purchase a walkie-talkie that is designed for that purpose alone, it would have limited usefulness unless you stayed in that country for an extended period.
The alternative is to purchase a programmable radio such as the Retevis RT22 or Baofeng GT22, which are the same radio, and program a combination of FRS and PMR446 channels for use onboard at sea and at ports of call.