Sugar, sugar, sugar, and more sugar.

The reason there were rum distillers to start with was the presence of the huge sugar industry. Between 25 and 40% of all of America's sugar pre revolution came from Cuba. The by products then we're where molasses came from which could then be distilled to rum. While the raw sugar could be exported.

Other major products included tobacco, the meme of Cuban Cigars is not by accident. Cuba still today makes up a huge part of the world's tobacco crop production. And coffee, along with cattle as well.