I've always fixed my own flats. I carry a spare tube and a repair kit. Usually I pile up flatted tubes in my garage and fix them all on a rainy day.

What amazes me are the guys you see on group rides who don't carry any seatbag, tools, repair kit or tube. Then they flat and expect someone else to bail them out. I don't mind helping someone out who's had bad luck, such as 2 flats on the same ride, but I am very reluctant to give someone my spare tube because they are too much of a weight-weenie to carry one. What happens if I get a flat after giving them my spare tube?