I thought of this thread today when I stopped to help a couple with a flat problem. The MUP repair stand pump wasn't working, so I was looking for a Presta-Schrader adapter. Although I was sure I'd have the adapter it wasn't there, although I did find my missing tire levers. I swear the tube looked like a Shrader (it wasn't, when I sorted it at home) and I had extra stuff like a rolled up zip tie, an 18650 battery for a light I didn't carry, some accumultated miscellaneous bits. I was wondering just how long it's been since I've been into the bag, and the discolored scuffed up CO2 cartridge was telling me "never", or at least not since I moved the frame pump to another bike.

How that is possible, to have no flats or other use for the tools in 1.5 years I don't know but the evidence is irrefutable. Since I'd never used the CO2, I thought why not use it now, there evidently being such little risk of my own flatting, and it worked like a charm. I was happy for the practice and to test that it still works truth be told, and rode straight away to a bike shop I like for a replacement. Excuse for a quick visit, I recalled a box of them at the counter but no price ... which turns out to be $5.96!

The moral is, check your tool bag from time to time, or it might wind up costing you $6 like me.