If you mean literally anything, I’d build a working fusion reactor that generates more electricity than it consumes, and sell them for about $10,000 a pop. I’d become so wealthy in a matter of weeks that Bill Gates would be a homeless bum in comparison. Plus, I’d have solved the world’s energy crisis and stopped global warming in its tracks. With everyone producing their own electricity at home (essentially for free except for the initial cost of the unit), demand for oil would drop to zero, and sales of pure electric cars would skyrocket. High-tension power lines that criss-cross the country would be a thing of the past, and there would be no more regional power failures. An enemy couldn’t knock out the whole country’s power grid by bombing a few major power plants. And nobody would have to worry about nuclear disasters (fusion plants don’t work like fission plants…there’s no danger of meltdown or explosion or release of nuclear gas into the atmosphere)
Oh yes, then with my new-found billions, I’d have sex…lots and lots of sex :-0