We can seriously address the global warming problem. This will first help the low lying nations that are in danger of being swept away by the ocean, but it will also help reduce other weather-related problems all over the world.
As to foreign policy—we can start talking to other nations, even the ones we call terrorist. We can also start respecting other nations. We can stop being the world’s bully.
As to the economy: we can stop using foreign aid as a way to give American companies more business, and actually use it to seriously develop other countries, by letting them make their own decisions about how to use it. It could be funneled through NGOs instead of foreign governments (sending it to foreign leaders just encourages rampant corruption).