I’m retired, secure enough to take trips totaling 3+ months out of the year. 1K more a month would mean a new car plus an extra month of travel.
Pay off debt.
First, the relatively little outstanding consumer debt, then car payments, then mortgage.
Middle class. The first two things that came to mind are more travel, and paying for labor help around the house, both for routine cleaning and for handyman type repairs that I’ve always handled myself up to now. There may be one or two larger projects around the house (aka “money sink”) that would see some of the money, especially if it continued into a second year.
I’m middle class; I live in a rented apartment, and I’d be destitute if I missed a paycheck.
I’m put it towards debt. Stupid debt. I should be out of it in just a few years, but this would expedite the timeline.
Barring that, it would first go to clothes (I’d like some custom tailored suits), then a travel fund (my goal is 2 vacations a year: one foreign, and one domestic)
upper middle and cruising toward early retirement. I would treat it as an annuity and adjust my cashflow projections accordingly and recalculate asset needs and placement for retirement…God, I just read that back and it is quite possibly the most boring thing ever written!
Accounting is infamous as a dry topic for a reason. 
Middle-to-upper-middle class, no kids/pets, no debt, relatively new car (a 2020 BMW with less than 30K miles, thanks to working remotely until 7 months ago), can responsibly enable my Lego and gadget problems, etc.
I should say that an extra $1000/mo would get saved, but I’m a renter and I know that I’d actually use it to get an even nicer place. I’ve always spent most of my income – sometimes more than I should – on where I live and what I drive.
As the saying has it
Most of my money I spent on wine, men/women (as one prefers), and song. The rest I wasted.
Home repair and renovations.
Middle class to lower-middle class. I’ve been gifting my adult child $7,000 annually for her Roth IRA, but can’t continue that much longer without endangering my retirement. A extra $1000/mo would handle that, and help subsidize an impoverished sibling, some overseas travel, and more charitable donations (Ukraine needs drones).
I have some money from royalties and book advances. The last time I put money in a Roth was ages ago. I do know you can’t move your RMD money into one.
If it happened my financial planner would shoot down anything stupid I suggest.
If the OP doesn’t mind, I’d like to extend this interesting scenario to one where you have to spend the money. In Unknown in the early 1940s, L. Ron Hubbard had an interesting fantasy story where someone was cursed and forced to spend $100 a day without saving any of it. So, no buying jewels, for instance. Not that easy to do even in New York.$1000 a month would be much easier, especially if it was really $12,000 a year, so you could combine a few months for first class air travel or a cruise.
Interesting. If the money must be spent on services or immediate consumption such as food or drink, that’s one standard. But any durable good has some duration and some resale value. Is that “saving” or “investing”?
Clothes, appliances, and cars all fall in that category. So does jewelry even if made of real gold and real gems. Those kinds of things aren’t good investments; e.g. you’ll pay 3x for a gold wedding band vs what they’ll pay to buy it back from you.
$1000/mo ~= $33 per day. Easy enough to blow that on a middle class restaurant lunch and a decent tip. If your workday doesn’t permit buying a lunch, you can do the same thing at dinner instead.
ETA: ref @frodo just below. …
I think where it gets hard is where you need to spend each day’s amount each day with no overs no shorts. It becomes a question for the problem-setter to pick a number that’s just too big to routinely dispose of in the approved ways, but too small to endow a rocketship development or really any commercial effort like advertising buying.
As I noted, $1,000/mo ~= $33/day ~= the price of one mid-level restaurant meal. Easy. Now make it $10,000/mo ~= 330/day. Much more difficult to dissipate that volume of money day in and day out. A fancy pants liquor store will sell you a $330 bottle of wine every day. But you have to drink it. Eventually your liver won’t be happy. etc.
All these “you have to spend x amount of money” scenarios are interesting but inherently flawed, all the story protagonist or Brewster in Brewster Millions have to do is buy airtime, TV advertising space in primetime in the priciest areas, you’ll burn your money pretty quickly.
(Although when I saw the movie, space nerd that I am, I declared that I would immediately spend everything in designing, building and launching my own rocket to, at least, LEO)
Yeah the rocketship example is more for Brewster Millions where he had to spend 30 million dollars in a month, it’s not enought to even start building but you could pay it to a space agency or (now) a private business to put say, your favorite astronaut Playmobil in orbit.
But the advertising trick ought to work:
Protagonist: “Hey network executive, how much airtime can I buy for 100 dollars a day?”
Network Executive: <$time>
Protagonist: “I’ll buy that”.
Forgot to add status- lowest poverty
Living an upper middle class lifestyle on a middle class income. I’d use it to pay down credit card debt.
I guess we’re upper middle class. It sure doesn’t feel like it. It probably would if our medical expenses weren’t so high.
My first instinct is to put it toward student loan debt. Barring that, investments.
But I’m also wondering if this would be the income we need to afford a mortgage. We could make a down payment, we just can’t afford a mortgage payment right now. I’d have to do the math, but it might work.
I might also make a small increase to the monthly allotted discretionary budget.
The easy answer is rent and/or subscriptions. The money is spent whether you use the asset or not with zero tangible equity to show for it.
Or throw a huge party. Rent out a football stadium. Invite the Stones. It wouldn’t be that hard.
It’d be a Dope Fest for the ages. Everybody gets a first class flight to the destination, and gets to stay in a 5 star resort. We could burn through the money easy peasy.