I'm usually one of the ones in a group ride who steps in and helps to change other people's flats. It goes faster with multiple hands. And among other things, I use my CO2 to help out. So I use it pretty frequently. Works like charm, every time.

For whatever reason, there's a minority of folks who show up to these group rides wholly unprepared. They just trust that the rest of us will have a tube and a cartridge and aa tire iron and.... These are in many cases friends of mine, and I try not to judge, but I can't imagine being that person.

People offer to pay me back for the tubes and cartridges that I donate to the cause of keeping us rolling. I never accept. Compared to the amount of money I spend on my cycling habit, it's in the noise. (But don't get me wrong - I'm not the only one on the giving side. There are others playing the same role.)