I drove 10,000 miles last year. I have a 16" tiny temporary donut in as my spare. I will not use it unless it is an absolute emergency. If I put it on the rear it will burn out my sure-grip, but something might happen where it will be worth burning out. Paid $20 for it at a junk yard.
If you have an EMERGENCY, how much would you pay to have something to throw on there? $20?, $100?, $500?
I also carry a small toolbox that has a mini floor jack in it. I have a bumper jack, but it is just in there for looks. I wouldn't use it because it ruins your bumpers. I also have AAA towing with my cell phone carrier, just in case.