I agree with Chris L. Carry 2 spares if you're really concerned. It only takes a few minutes to swap out a tube.

A friend recently dropped off his bike for me to do a spring tune up on. I noticed the rear wheel was pretty out of whack so I decided to put it on the truing stand and get to business. When I tried to let the air out of the tire, liquid started spraying out of the valve and then nothing at all, air included, with about 40 or 50 pounds still in the tire. After monkeying around I finally decided the only way to remove the tire was pull the valve stem off, destroying the tube. When I did this I was greeted with a nice stream of sticky liquid all over my shoes, his rim, hub, and spokes, and my garage floor. Now I know why garage mechanics hate fix a flat in car tires.