A couple more comments if I may. Yes a few times I have stopped to help someone, they did have a new tube, but really didnt know how to use it.

Then as to carring a spare tube. ONe time when I flatted, I patched the tube, but the presta stem broke off when I was inflating the tire. I of course replaced the tube, and used my CO2 cartridges to inflate the tire. Now I always use the CO2 and just carry the mini pump as back up. BTW I have had at least 2 mini pumps fail. For Christmas I have a mini pump with a small hose and gage on my list so as not to stress the presta stem. I will still carry CO2 mainly when riding with a group for faster repair so as not to hold up the ride.