You are given a a million dollars if you can spend it in one day. The transaction has to be finished that day, so no houses or similar. What do you buy?

9am Porsche dealership, point at whatever the most expensive one in the showroom and say "I want it and I want it right now, how much? Ill bring it back for its first service tomorrow but I want to drive it out right now" drive it straight to the Audi dealership and repeat at the BMW dealership, if I have enough money and time left, head to the Honda dealership and grab a Type R.
The following day, drive the cars back to the dealership, say "I know I'm going to take a loss but I've changed my mind. Can you buy the car back?"
Probably wind up with about $700,000 and I'm not taking back the Type R.

You know... there's an old movie about just this topic called "brewster's millions"

How many school lunch bills can be paid with that?
Or tuition for how many community college students?

Why no houses? I'm sure I could find a house that they could sign over that day if I paid the whole million in cash. It'd be a shithole anyway, if it's only a million bucks.
I guess I could buy a million dollars worth of shares in something that will likely go up by a few cents if not a few dollars the next day, so I could immediately sell the shares and would have more than 1 million.

Medical debt. Just buy up as many people's medical debt as I can.
- Your halo is in the mail.
- This is fucking brilliant! I'm in the UK so not to rub it in, but we have the NHS...
  
  So? Buy delinquent credit card debt.

Go to all the dealerships in my town and buy up as much inventory as possible. You can purchase the cars that day and pay cash in full but you won't receive them for a while. While you wait you have a few days to weeks to coordinate with as many groups as possible to "give" those cars to families in need assuming they can cover the cost of insurance for that vehicle.

My partner is not an artist, but he could paint something on some nice paper in a few minutes. Buy a frame, give him the rest of the $1mil, proudly display the piece in our house. I trust him to use that money well.
- This is genius!!! If he's not willing to do it I selflessly offer to help you for a 10%. But only because I'm altruistic
- Ah... Brewster's Gambit. A classic move.

1 million dollars... worth of pudding.
- I like your style. You could travel through the city bestowing pudding on everyone

Well, being is that I already have all of the equipment set up, I could just pay off my house and all of my debts with the remaining, I don't know, $600,000 just buy jewelry and cars that I can then resell in the future or something if need be.

Is this a "Brewster's Millions" scenario, where it has to be wasted, or do you just have to buy a bunch of crap?
Also, I'm presuming you aren't counting time for the check/etc to clear. Otherwise, very few of us could ever even conceivably make that level of transaction.

Stocks
- Stocks are currently T+1, meaning the trade does not finalize until the next day.
  
  In my country they're finalized immediately

Take out a loan using the million dollars collateral and then pay it off with the million dollars?

There's basically nothing I could buy and have it delivered in the same day anywhere near that amount unless you count stocks or something.
My first instinct was solar and battery for the house, electric car, new tractor, farm supplies, and home improvement (japanese houses aren't great and I would basically gut and rebuild my house as a net zero at least passivhaus).

I would buy myself a nice camera and several lenses (easy $200K right there), a new phone, and a new car. I would then donate the rest to the local homeless shelter.
- Donating really doesn't feel like it adheres to the spirit of the question tbh. Frankly I bet if I had a solid 24 hours during the standard work week and a million in cash, I could get a home sale closed, though. Without mortgages, as a buyer I can skip inspections insurance etc and I'm fairly sure it could be done.
  
  That's a good idea, but could the solicitors do their side? Although for 25k I bet you they'd find a way
- 200k on camera and lenses must be for some really exotic stuff? What do you have in mind? Sony A1-2 + all the lenses on the first page of G lenses only got me to 90k. And thats a crapload of useless lenses given you can't really carry 15 lenses everywhere with you?

There's a lotus dealership up the road, or a Corvette dealership a little farther. Honestly I'm very close to several luxury car dealerships so I would just buy a few cars.

Easy - index funds.
- Usually takes a couple of days to go through no?
  
  Depends on your broker, but generally they can process same day