You get to keep only enough to maintain a very modest lifestyle in a low-cost-of-living area, the rest of it has to go towards improving the world in some way.
Edit: Given the previous rules that you must maintain a very modest lifestyle in a low-cost-of-living area, would you rather choose to opt out and not have the money at all?
Expand food banks and shelters. Then donate water to places that need it.
This completely. You cant end capitalism with that kind of money, but you can provide cheap or free alternatives to basic needs to force the price-gouging vendors to actually compete for once and align their businesses better with the consumer.