I've flatted a a quarter mile from my front door, and 20 miles from home with no bus route nearby, in the dead of night - rolling on ultra-gatorskins. Seems I almost always get the slow flats that you come back to find after the bike has been parked for a few hours. As a result of this luck, I carry either a backpack or panniers with patch kit at all times (it's also AZ, goats head capital): Usually two CO2 cartridges, CO2 nozzle, a tiny hand pump (that doesn't do crap), some patches, at least one tube and two levers - oh and a 15mm wrench (no QRs). This doesn't account for the multitool, spoke wrench, etc. in case of mechanical issues, which I generally try not to leave home without either.