I carry a tube, patch kit, levers and pump, but I rarely flat. I change them for my housemate (rare that she goes out without me, and I usually go to her triathlon events). I have taught her, a couple of times, but I do it faster, so I usually just jump in and do it to keep us moving (and her hands clean...)

I was riding along a MUP about a month ago and ran across a teenager walking an old 3 speed with a flat.

Me: "Need help?"
Kid: "No, I just have a flat"
Me: "...Yeah, but do you want a hand?..."
Kid: "What would do you?"
Me: "Replace the tube... I have one right here" <-points to pannier
Kid: "Oh. No, that's ok. I need to get to school."

It was a very strange interaction, it left me trying to decide how he thought getting to school walking a flat tire would be any faster...