The MKZ has a donut, and yes it has been used.
I have a full size in the MG-it's an old tire on a rough rim. I really should throw a $40 China special on it, but figure it will get me home if needed. I keep one of those 2 ton floor jacks in it also, as they're small and I consider the factory jack for the car unsafe.
I check the air in these periodically, although we do have nice Stanley jump packs with compressors in both cars. Still, though, the last time I checked the donut in the MKZ it had been a while since previously checking, and it was at 25psi. I'm glad I did as it would have been useless at that pressure, and it took me a long time to get it to 60psi even using my air compressor.
My wife's Jeep Compass has a 12V compressor that can "inject" slime(that's contained in it) and then pump the tire up. Not too long ago, I bought a tire plug kit(and also have a nicer one in my tool box) to keep in there.
This is actually timely as lately I've dealt with a run of flats
1. About a month ago, my sister in law calls with a flat in the garage(2018 Jetta). I go over with a jump pack after work that afternoon-she'd driven her husband's car, and I went and met him over at their house before she got home. We pump it up-not as fast as if they could have come to see me-and it won't get to the 37psi on the door sticker with the jump pack compressor. As I shut it off, we heard air hissing out and found a nail sticking out the sidewall. She due for new tires anyway, but of course there was no spare to have a good way to get it to the shop. I'd not brought any real tools with me, so offered to come back. I know you SHOULDN'T patch the sidewall, but in this case I figured it was safe for a ~10 mile low speed trip to a tire shop. I ended up not doing it-her father in law decided that they should just air the tire way up and drive it there-I bowed out of that one.
2. Last week, my father in law calls. He'd been leaving for work that morning and apparently picked up SOMETHING because it was fine when he pulled out of the garage, at ~25psi by the end of the neighborhood when he decided he should turn around, and flat by the time he got home. I loaded up that afternoon with my smaller(8 gallon) compressor, which is great for inflating and will also run an impact intermittently, plus a full size floor jack, a couple of stands, an impact, breaker bar, torque wrench, and a few other odds and ends. His is a 2020 Buick CUV of some sort or another, but surprisingly had a donut. He wasn't home when I got there, so acting on instructions relayed through my wife, I put the donut on. He has 20K miles on the factory Continentals, and when I inflated I found a nice nail-sized hole in the tread.
Around that time, he got home from work, and after discussing a few things with him we decided to put a plug in for him to drive to a shop and have it looked at. Off came the spare, on went the plugged and inflated regular tire, and off he went to a tire shop. They looked at my plug, said it was as good as they'd have done, and sent him on his way. He's still driving fine on it.
3. Just yesterday afternoon, I'd been working on my MG in the garage-I'd been chasing a disconcerting clunk and found it in an even more worrisome place(one of the brake caliper bolts was missing). In any case, to test drive it, I pulled my wife's car out of the driveway and onto the street, left it there while I circled the block a couple times in the MG, and then reset everything. An hour later we come out to go to dinner, and her front right tire is flat.
So, since it was right in front of the garage, 5 minutes later I have the wheel off the car, and sure enough there's a nice clean hole in the tread. Back before we were married, she needed 2 tires, and the shop had sold her Dorals. They weren't great tires anyway(when I looked at them I said "you bought WHAT?") and when I had that one off yesterday I declared it EOL.
In any case, out comes the plug kit again and of course it all goes back together. We end up driving it to dinner and it was fine, but she agreed on the new tires-4 this time. One of the shops she'd called while I was working said that they could work us in today if we got there early in the morning. Of course she had to work today(she's a nurse, which means leaving at 6:00AM and usually not home until 8:00PM) so she drove my car to work, I got to the tire shop at 7:00, and went back at 8:30 to pick it up with 4 new installed.
Short answer on this, though, is a plug kit has been handy more than once. I don't consider plugs or Slime a permanent fix, but they're probably as good as Donut for getting you to get it fixed, and unlike donuts they drive like a regular tire.
My wife has already put spare tire at the top of her shopping list for the next car, though. I keep meaning to see if I can find at least a donut for it. It does have a tire well-that's where the pump and all the other odds and ends are kept-and I think it MIGHT be big enough for a full size.
In a broader sense, I think it's funny how we use to complain about donuts and on my vehicles prior to the MKZ I'd actually gone and bought a straight but ugly junkyard rim and mounted cheap tires on them so I had full size spares. I was fortunate to have full-depth tire wells. Now, it seems even a donut is a luxury.
