STAN'S NOTUBES TUBES/GLUE
It works for cars, so why not bikes? Just like that fix-a-flat stuff you wonder about using, this milky goo seals small leaks and punctures, up to 1/4in. And the stuff works really well. The kit can convert most tubed tires to tubeless. And if you're already riding tubeless, it makes running low pressure and riding through thornbushes, glass gardens, and herds of goathead thorns all the safer.
For those who are wondering, no the sealant doesn't freeze, doesn't alter the balance of the wheel, and can work in any kind of tubeless tire when combined with a UST or tubeless-ready rim. If you have a standard clincher wheelset, bear in mind that you'll still need to prep your wheels with a tubeless conversion kit before taking advantage of this sealant. The one-quart container can seal up to 16 tires.