Oh man, idk. The idea of being a leader of a country, scares the living hell out of me. If I could do anything, I would try to give every citizen a stimulus check, help out small businesses, help with water problems in flint mi and any other places that need help in the US.
But for just a day, you're not going to be able to do a whole lot there. In order to really do anything, you'd need months and years as a leader.