They can do a lot. They can use much of the unused lands to grow crops to feed their populace while also hiring their unemployed masses to work the fields; they have so much land that they can grow different crops all year 'round, to feed the populace and export. They can also raise cattle for beef and dairy, and use the milk for different dairy products, for school programs and for the poor, particularly the malnutritioned.
More people working the fields and diary farms will also help them pave roads to improve transportation, for eduction and eventually trourism. But the basics are always to help their own before considering exporting products. The same goes with Santo Domingo and Haiti, both.