Always equated using some else's snorkel to wearing someone else's underwear. A mask that fits with a properly attached snorkel is reasonable and will last if you keep the salt and chlorine rinsed off. Definitely need fins but those you can rent or borrow to avoid having to pack. If you intend to SCUBA, seriously consider using your own regulator that you know is clean and working. You can rent the rest. A lobster bag is a cool way to carry your gear to the beach, besides coming in handy if you find something. Picking up shells is usually forbidden, except Puerto Rico where you can get away with anything. More than you ever wanted to know.
I was once poorly fit with fins and, by the end of the first day, the skin on the tops of my feet was worn raw. I could barely wear shoes, let alone snorkel comfortably from then on. Since that time, we always bring our own equipment. At least I know everything fits and I know whose mouth the snorkel was in last.
We accumulated the equipment over 2-3 years, giving it as gifts to each other for birthdays, Christmas, etc. We were only able to cruise about once every three years then so there wasn't any hurry.
We bought quality equipment from a local dive shop, with proper fitting and selection done by the pros. We probably have about $250 each invested, but it's worth it since we snorkel at almost every port. It's especially worth it now since we can afford to go every year.
We pack everything in a separate suitcase with little else inside. That gives us room to bring back whatever we buy on the cruise. We carry the equipment in a nylon mesh bag when we go to/from the snorkeling site.
I agree with 10x.....take your own if you have it. I have seen some very grotty equipement available for hire, you also have the problem of finding the right fit & some places do not have fins at all....and as for life jackets!!!!!!!!! forget it, no way would I trust my life to a hired one
Bring your own. It's really the only way to be sure that the equipment is clean and/or sanitary. The added benifit is that it is cheaper and the equipment is fitted to you. Unless you are an expert type swimmer then fins are the only way to go, you would be surprised at just how much they help. I've done both and even though I have been swimming and diving for over 40 years I much prefer fins and the only reason I don't always use them is to save space or carrying them around.
Renting the equipment on the ship for the week was more expensive then the mask and snorkel sets we bought at home. You can generally get a decent mask and snorkel set for about $30-40 at a sporting goods store, which is what they charge to rent the stuff on the ship for a week. No use in paying more unless you are going to take up snorkeling.
Most of the excursions provide equipment but I don't want a "used" snorkel. I'm just funny that way.
Personally I don't like fins, they just get in my way but it is totally a personal thing. My feet are plenty big to propel me through the water and it is a better work-out.