re: When was the last time you changed a flat tire ?

Don't change them unless necessary. I carry a plug kit and a small compressor powered by my cigarette lighter plug-in.

This only works if the offending nail/screw/metal is in the tread portion. Pull the nail, ream out the hole with the supplied rasp, slip a strip of the plug material in the tool then push it in far enough to go inside the tire and quickly pull on the tool to remove it but leave the plug in the tire. Then air up and be on your way.

I've done this dozens of times on both my truck and the wife's car with no problems.