i ride with a CO2 pump and 2 cartridges. if i have more than two flats in a given leg of my commute, i'll simply hop on the el or hail a cab. i ain't fixing 3 flats just to get to work in the morning.

to date, in 4 years of commuting, i've never had more than 2 flats in one leg of commuting (knock on wood), and even that has only occurred twice in over a thousand rides.