Dude I took the same cruise a couple years ago on carnival. Left galveston and went to jamaica, grand caymen, and cozumel. It was pretty awesome.
I debated taking some with me, but I had to fly from michigan so I finally decided to take a tolerance break. Once we got past the airport though security is a breeze. No drug dogs, and no thorough searches getting on the cruise ship. Getting on the ship at ports is a joke of security, absolutely no risk of getting busted unless you are smoking it. Getting on the ship initially was also a joke. Getting back through customs once we got back was a bit more thorough, but I could have easily gotten through that too (but why not smoke it all while on the ship?).
I would not recommend taking weed through the airport. You probably have a 99.9% chance of getting through with it, but 0.1% chance is pretty high I think. If you aren't going to fly I suggest you roll up enough to sustain you for the entire trip, seal it up really well, and crotch it. Board that cruise ship with a very secure package under your package in tighty whiteys. Plenty of opportunities to be alone on the ship and blaze on the open ocean. Or you can sneak a doob or two off the ship when you go onto the islands and find a spot to blaze up. Or bring enough to do both.
I also recommend going to buy a cheap underwater mask and perhaps a snorkel from walmart. A lot of people don't like grand caymen all that much - I didn't explore it too much, I just went swimming with my mask and underwater camera and saw tons of tropical fish just off shore. It was like a shore excursion to see colorful fish but totally free!
I did the zip line in jamaica and it was awesome. Other than that jamaica was an absolute shit hole. The port we stopped at was gated and we were not allowed to leave without hiring a guide. If you could take a 100 mile long shit, and plop it in tropical waters, then get a bunch of poor theiving niggers to live on it and take advantage of tourist you'd have a decent substitute for jamaica. Absolutely worthless country that I will never go back to.
Also don't expect to find all kinds of cheap prescription drugs in Mexico. Everyone always told me you can get any kind of drug you want for dirt cheap because everything is totally unregulated. Not true at all. You cannot buy ANY narcotics over the counter. You can buy antibiotics and I think you could get viagra (not positive on that. I didn't buy any), but it was not cheap. If you have insurance of any kind you will be far better off obtaining drugs legally in the US through a doctor and pharmacy. I suppose if you know you have a bacterial infection, and have no insurance, and happen to be in mexico, then it might be beneficial to visit their pharmacy. Other than that it's a waste of time in my opinion.
