I carry a couple spare tubes in my kit so I can just swap them out quick if I'm on the go, but also have a patch kit on me for those really bad days where you can seem to go 5 minutes without getting another flat. The punctured tubes I just keep together until I have a bunch of them, and just patch them all up at once.

Also, you can get the patches really cheap online, and a tube of vulcanizing glue lasts forever.