I was driving my old pickup truck home from town this AM in steady mid-40F drizzle on a local Hill Country road when I saw a cyclist on the roadside, rear wheel off and cell-phone in hand. I pulled over and asked the obvious "You OK?"
Hypothermia is no joke, this very fit guy on a local club with lots of experience had flatted and shot both CO2 cartridges into Bexar County's atmosphere with zero effect on his flat. That will not get you home.
He sat with me listening to Steve Earle w/ the heater on full until a friend came out to drag his wet *** home.
Some things here:
1) Always carry a pump, they reliably put air in tires. Bring CO2 also if you feel the need.
b) Carry your 'phone, if someone will come and fetch you in inconvenient remote rural spots at odd hours.
iii) You are next.