The woman who sells you fish uses that money for school fees. The school pays a teacher. The teacher buys from the man who fixes generators. He buys fish. That is a loop, and the longer the money stays in it, the stronger everyone gets.
None of this is sentimental. It is arithmetic.
Buying local does not mean settling for less. It means looking here first: the artisan down the road before the stranger across the water, the neighbour's listing before the far-off one. When the local option is genuinely good, say so, loudly. When it is not, tell them honestly so they can improve.
An island economy is a set of habits. Change enough small ones and the whole thing starts to look different.