This is how you sneak liquor on a cruise with a sealed Listerine bottle.

Storytime! (kinda related)

When I was a stupid 18 year old, I went on a cruise with my family. The first stop was in Cozumel. Being the reckless young man that I was, I immediately found a street vendor selling beer. I was of legal drinking age in Mexico, so I proudly presented my ID and purchased two Sol beers and took my free tequila shot. Since this is my first legal alcohol purchase, I far overestimated my ability to drink and interact with the general public in a foreign country. It felt wrong to be walking around in a crowded area at 18 while I'm double-fisting beer, so I drank quickly and wandered through the shops further away from the touristy area until I find a secluded little shop with nothing but intricate glass "tobacco" pipes.

So as I drunkenly stumble through and marvel at all the beautiful glasswear, I get the brilliant idea to ask the local smoking accessory purveyor where I might locate something to put into his lovely smoking pipes. He seemed shocked at first, but he looked around to make sure we were the only ones there. He tells me, "You know that is illegal here?" A few moments pass in silence as my inebriated brain pieces together that I have quite possibly fucked up big time, and I'm getting ready to run when I hear him ask, "So, how much do you want?" I asked for a quad, I was told that I basically needed to buy nothing short of a trashbag full of weed to buy from his connect and that I needed to get out of his shop.

TLDR; Got drunk in Mexico, tried to buy weed, (kind of/almost) succeeded.

To more directly address your question, it's not extremely difficult to get it on the ship. They shuffle everyone through a line like cattle and quickly inspect your belongings. As long as your bag doesn't stink from a mile away, nobody's gonna notice if you put forth any effort to hide it. In hind site, I could have rolled some blunts and just took them in the pack without incident. The problem is that it's gonna be impossible to smoke anywhere on the ship. This leaves edibles, having enough friends on the cruise to smoke a trashbag full of weed, or (gasp!) not getting high for the several days you're on vacation.

As long as you don't have anything when you come back to Murcia and go through customs, it's not a big deal to bring weed with you, but coming from someone who makes a lot of poor decisions, it's not worth it.

Anyways... Time for a blunt.

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