Call me an idealist 🙂 but, I would put together a group of people to decide the science policy of the whole world. If every country came together to work on a few huge projects (like CERN) we could get them done a lot faster than any one group working on their own. A few of the many projects I would like the world to collaborate on are:
-harness enough solar power to power the whole world (cars, trains, cities, agriculture, etc…)
-health research to allow us to live healthier for longer, rather that trying to extend life overall
-research new systems of government to distribute resources fairly to everyone
-keep trying to answer questions like where did we come from and how does the universe work?