About once a year I take one of my old tubes and a 1/2" arch punch and reduce the tube to a bunch of 1/2" circles. That makes about three lifetimes worth of patches, but as long as I'm whacking the thing I might as well do the whole tube. I rinse the circles in a bit of acetone to remove the talc and let them dry, then throw them in a bag.

I carry a dozen or so in my kit and, when I have to patch a tube, I take one out, lick it, wipe it on my jersey, put some glue on the back and on the tube, and then put the patch on the tube and wring it in. It's a ****load less fiddlin' around than a commercial patch and works just fine. I have been doing this since dirt was new.