The last time I rescued a guy, he had a can of Fix A Flat hanging out of his flat tire.
Fix A Flat was a great option 20 years ago or more when it came out, but now its old school with too many shortcomings. It freezes and over time the pressurized gas leaks out. Its limited on how much gas it has even at the best of times so if the leak is above a point, you won't get a full fill even if it stops the leak. Last but not least, it dries hard as a rock and if you aren't running the tire till it dries, it will put your tire out of balance. It gums up both stem valves and rims to the point many tire repair places won't repair the tire. Those that do won't be happy.
Its really not that hard to fix the tire and not that much more cost. Buy yourself a low cost electric pump and tire plug kit. Find the leak (pump and use water looking for bubbles), remove the cause, ream it, plug it, snip off the excess, then pump it up.
Slime sells a nice little pump with a bottle of Slime for $20 at Walmart. Add another $7 and buy a plug kit.
Slime is a tad harder to use than FixAFlat in that you have to remove the stem valve, it comes with a plastic tool to do that. You then pour the Slime in, replace the stem valve, then pump it up. What it doesn't do is dry and setup hard. These new cars that because of their advanced stabilization systems don't have spares, actually come with a pump and bottle of slime.
For real security, you can do both, plug the tire and slime it.
I've had so many issues with FixAFlat over the years, I absolutely not only don't recommend it, but recommend against it.
The guy I rescued didn't know where his leak was, didn't remove the screw, and because he wasn't lucky enough the leak was on the ground side of his tire and he didn't want to run his tire flat on the rim, the FixAFlat did nothing for him. I felt sorry for him sitting there watching that tire go down with that can sticking out of his stem, so in ten minutes, pulled his screw, plugged the tire, and pumped it back up for him.
Tj