In many areas of the
Caribbean or
Bahamas you will be lucky to find any milk at all in stores, and it will mostly be long-life stuff. Having said that, I wouldn't be surprised if you could find it in large supermarkets near tourist places, though I haven't looked. Basically, the
rule cruising is if there is some
food stuff that you absolutely have to have you must bring your own supplies of it as you can't be certain of finding anything when you need it.