I’d buy a billion people a taco.
I’d commission The Barenaked Ladies to re-write that song.
Your first call should be to a lawyer, but that would not be the worst thing.
I am in agreement with a lot of people in that with a billion dollars, I would become a philanthropist. My full time job would be investing the money in a safe manner and then turning the profits into social good. I would try to keep my giving a secret - I want no credit at all, not so much as a mention - but that might be hard to do. I’d try.
Of course we’d go on vacations and drive nicer cars, but our tastes aren’t expensive enough to make much of a dent in a billion dollars. I’d make us live off an allowance paid for from interest.
If I were really able to chase after interests I could easily spend far more than a billion and would really have to severely limit myself. I would want probes for all the major known Trans-Neptonian objects, but would have to limit myself to maybe 3 or 4, for example (and a proper orbiter instead of a flyby would be much more expensive, even further limitations.) If I skipped the space exploration, I’d love to build a world-class Natural History museum here in my home state. I don’t know exactly how much it would cost to build and furnish a world-class science museum, but I’m thinking at least a few hundred million (and would probably run at a loss and need a foundation to keep the doors open.)
For personal use, even 10 million is more than I would use in the rest of my life if I had it, but for scientific/cultural interests, a billion is kind of measly.
I also would not really want a billion to fall into my lap. People can have their opinions about the ‘social value’ of what various self made billionaires have done but from those people’s own POV they worked hard to create something. That’s missing if it’s a pure windfall. Which perhaps could be applied also to inheriting a billion but in that case you’ve probably grown up used to the idea.
It would not, I believe, make me think I’m special. The problem would be the feeling of obligation I’m pretty sure I’d have to work hard to make a positive difference in the world with that money. But that’s not what I really want to do at this stage of life (retired, financially comfortable). It would be a burden.
Lesser still very large amounts would be fine. 
Where it would turn negative is amounts so large I’d feel overwhelming obligation to make a ‘big picture’ difference with the money.
I’d like to start a program at schools all over the country. The kids would contribute an answer to a question like: “how best could a million dollars improve your community?”. The kids would vote on it, and when the plan was implemented, would manage the funds. They’d learn all kinds of civic and financial lessons.
First step is to tell my wife but nobody else, and ask her to keep the secret as well. Next step is to pay off all our debts. I’d buy a few nice things like a new car for myself and another for my wife (high 5 digit to low 6 digit range) and a new house in the same city where I currently live (around mid 6 figure range). I’d quietly pay off the debts of other close loved ones in those situations where doing so anonymously is possible. This would include immediate family and very close friends only, not second cousins of my brother in law’s next door neighbors best friend or anything like that. I’d have time to pursue the things I want to but don’t currently have time for*. Of course after all that I’d still have somewhere between 998 and 999 million.
Then it would be time to start looking into charitable works. I’m the type who would want to be more hands on while remaining anonymous so I’d set up some kind of foundation. I’d probably focus on environmental causes, things like purchasing environmentally sensitive areas that someone else wants to ruin by developing, and purchase that land and set it aside to remain wilderness.
*. My hobbies aren’t very monetarily intensive but also boring so I’m listing them down here. They include reading fiction (horror and suspense), playing video games, and learning about things like quantum mechanics. I’d probably have a few more expenses in these areas, but probably nothing that would add up to more than one or two million dollars.
I do know that I would definitely spend and/or donate most of it. To me, money is only worth what it can buy. If hoarded, it’s nothing more than a bunch of impressive numbers.
ETA. I had one other idea. It might be beneficial to tell people that you won a million dollars but that after paying off your debts and spending on a few minor luxuries most of the money is now gone.
If I came into a billion dollar windfall, the first thing I’d do is consult with an attorney and figure out how in the world to stay as anonymous as I possibly could.
Second, I’d invest it for the meantime in much the same way that Dinsdale describes- several capital managers and auditors, all from large, established firms.
I’d probably earmark some portion of it for personal use(maybe 200 million or so) and then set about using the remainder to endow some sort of charitable foundation- not sure what yet. Something that could be done with about 25 million per year investment income, as I’d want to reinvest some of the income to grow the endowment and eventually raise the charity’s scope or reach.
With my remaining 200 million, I’d probably take a couple of million as “fun” money, and travel/spend it on relatively frivolous stuff. The rest would be for retirement, everyday living, etc… One thing I’ve fantasized about would be to rent a space in a light industrial area with a large garage door, and floor drains, and make it into my “man hobby cave”, where I’d have cool homebrewing equipment, a woodworking shop, smokers, grills, etc… and a large airconditioned home theater type area with a game console, a office with a super-tricked out PC for games, and a crazy-fast internet connection- like maybe my own OC-12 or higher to connect it all.
I’d buy Greenland.
It’s for sale, isn’t it?
I would use the bulk of the money to purchase a majority stake in an NBA franchise. The Memphis Grizzlies last sold for $350M, and while the value of that team has increased I’m guessing somewhere around $600M would get me the whole thing, inclusive of the stadium. The rest I’d divide into four chunks of $100M - one chunk each into trusts for my two children, one chunk for charitable donations of various shapes and sizes, and one chunk in a very low-risk account to live on in case the Grizzlies thing doesn’t work out.
Like, good USA dollars, or small, Hong Kong dollars not even printed by their government?
I still think you guys are massively under estimating the lifestyle inflation that will happen when you are a billionaire.
Once you start flying private and get used to the truly first class travel you aren’t going back to TSA groping and tiny coach seats.
I would hire a man dressed as a smurf to follow my friend Keith around everywhere he goes.
When you’re a billionaire, you don’t need reasons.
Actually, this, I’d do. I’m already used to it. My company used to have its own terminal and plane fleet. I really, really miss this.
Step 1, hire a lawyer, get personal liability insurance
Step 1a. Hire the proper mix of professionals to help manage the money
Step 2 deteemine the amount needed to live the remainder of my days uninhibited by finances but without comspicous comsumption
Step 3 establish a trust for each of my younger family members just starting or getting ready to start out in life in order to give them a little help being independantly successful in life
Step 4 give the rest away (I even already know which charitable organizations will recieve the money) this amount should be somewhere close to half the money, possibly a little more
Eta step 1b hire a “preposting proofreader”
I’m not so sure. Having the use of someone else’s private jet would be good. Owning and operating one would be a pain though. You have to arrange all the stuff that airlines do in the background that you are completely oblivious to. Overflight charges and permissions, customs and immigration, maintenance, pilots, cabin crew, etc etc. All for something that you might not even use that much.
I think it would be better to charter business jets as and when you want to. Get all the benefit without the hassle.