Not much. Save it and be happy that my future is (somewhat more) secured. I probably wouldn't invest it in the economy, because the economy and civilization is going to crash in the foreseeable future due to our rampantly unsustainable treatment of the environment that we intimately depend on. Gold might be a good thing to invest it in, but then, if everything collapses, how will I defend and carry my huge stash? I could invest it in materials way more precious than gold, but would there be an availability of people able to assess their worth and a market for them in post-apocalyptic society if it comes to that in my lifetime? In reality, I'd probably just keep it all in a bank account and hope the bank survives for the rest of my life. Oh, and I'd also buy a 2"x2"x2" tungsten cube. I've always wanted one of those.