You're a miles from anywhere and you get a flat tire on your bicycle. The glue in your patch kit is dried out, you're out of CO2 cartridges, and you don't have a spare tube. What do you do?
The usual recommended solution is to stuff your tire with dry grass and leaves. I've never had to do that personally, but people who have done it tell me it can work well enough to keep from damaging the rim, though shoving the tire onto a grass stuffed rim can be a challenge.
I have tried this solution offered on Life Hacker, which is to tie the leaky area off with some string. I wasn't able to make that trick work, but Your Mileage May Vary and if you're desperate it doesn't hurt to try.
You should avoid riding on a flat tire. You can damage your rim -- if you flat it's likely the rear tire and the wheel is generally the second most expensive part of your bike after the frame. Your tire will also easily roll off of the rim, causing you to lose control even at slow speeds.
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I usually just use my handy-dandy IPhone flat tire app. It's called phoning my wife for a pick-up. Haven't damaged a wheel yet.
In the 1990s Specialized offered some tubes made the old school way from the dawn of pneumatic tires: a long sausage of rubber that you could stuff into the tire casing. Especially handy for bolt-on wheels or other situations where it's a pain to remove a wheel, you could put it in with the wheel in the frame or fork. Such a tube might come up short, leaving a soft area of unsupported tire, or long, causing a bunched-up area. If you cut our damaged tube at the punctured area you could tie the ends to create an air chamber. Then use your frame pump (never runs out of CO2).
You would lose a lot of tube to the knots, but tying the rubber would be more air tight than using string.