I carry as little as possible, and I get the sense that my fellow city commuters are doing the same. What that means depends a lot on the nature of one's job and the work facilities, though, so it's hard to generalize: some of us are lucky enough to be able to wear whatever we want at work, so it's simpler for us than for people who need to dress like grownups. I don't get the sense that most people carry a ton of fixit gear -- you're in a city, there are many bike shops and also public transit, so there's less need to be able to repair it right on the spot with gear you have on hand. But I'm not peering into people's bags either.