with modern tires a flat is rare (yet to have one on the TR3).
You must do a much better job of staying away from industrial areas than I do, then. Just a few months ago, driving past the Mobil refinery in Torrance, I picked up a huge chunk of metal in the left rear. Looked like maybe it was originally a tie-down strap on a semi trailer or something. 1/4" rod perhaps 3" long, bent into a U shape. The tire was flat by the time I stopped to investigate the noise.
On top of that, the spare was very low. I thought I could use it to drive the 100 yards or so to the nearest filling station (right on the other side of a 6 lane street from where I stopped), but it rolled off the rim when I made the U-turn. Arggh! Fortunately, the filling station mechanic was able to put a plug in the original tire (even though he couldn't remount the spare), so I was able to get home.
Few years before that, on my way to a date with my (now) wife, I had two flat tires in the same trip! A bolt punched a hole while driving along a trucking corridor, then no more than 10 minutes later there was an accident in front of me on the freeway and I failed to adequately dodge the flying debris. Not a good way to start a date! After dinner, she drove me to buy a tire at Pep Boys.