I occasionally do loops around where I live that don't take me farther than a mile or two from home, when I don't have time to ride any more than that. I still carry all or most of my kit out of habit but when I actually think about it I don't carry anything. Whenever I don't know where I'll end up, or set out to ride farther away, I typically carry a couple tube patches, a tire boot, tire levers, a tube, a couple co2 cylinders and an inflater.

The one time I didn't carry a tube, the flat I got was due to my tube's valve shearing off. I called my wife on my cell and I pushed the bike a mile or maybe two up the road by the time she got to me. Another thing that sucked about that incident was that I was riding on a designated path and at least a dozen other bikers rode by me, none of which asked if I needed anything.

I think a cell phone to call for a pick-up is the best thing to carry, because all else just might fail.