From your list the things I would include are:
Bolt snap, just 1
Zip ties
Spare mask strap
Spare fin strap, just 1
Spare mouthpiece, questionable
Spare computer battery and changing tool
Erik
Spare mask strap? Get a neoprene strap instead, no spare necessary
Spare fin strap? Not necessary, get full foot fins... it's the Caribbean. I've used the same pair of FF fins for over ten years. They last almost forever if you take care of them, and there's no straps to break.
Spare mouthpiece? Only thing on this list that might actually need replacing. But so extremely rare it's not even worth bringing. The dive ops all have contingencies covered.
Spare computer battery? Not necessary. Most computers (at the least the ones I've seen...) have a low battery warning, and the computer is good for more than a week of diving while on "low battery". So if the computer is fine before the week-long cruise, it will not need a new battery during the cruise. Now if it's one of those eight month, around the world cruises... then yeah, bring a spare battery.
My opinions are based only on my experience of having dived from cruise ships regularly since 2008. I won't take it personally if people disagree with me or even if they think I'm a reckless idiot for not bringing these "save a dive" items with me on a cruise & dive trip. Just felt that advice based on actual experience was worth sharing. The title of the thread seemed to ask for opinions, so I'm giving mine.