Just as a thought (coz it happened to me): I Used to use cartridges, and a few times on my daily commute I've only had 1 cartridge and 3 days til pay day and I prayed the whole time nothing would happen. If someone had needed my last cartridge - yuppers, they'dve had it. My thought is: that could be me someday and I hope someone out there comes along and helps me. I now have a Road Morph and have stopped several times and loaned them my pump and told them to save their cartridges in case someone isn't around the next time.
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways, champagne in one hand, strawberries in the other, body thoroughly used up, totally worn out and screaming: "Yeah Baby! What a Ride!"