I carry two tubes at all times and I don't patch on the road unless it's my third flat for the ride, and yes, that has happened.

I take the punctured tube home with me and every once in a while I take the time to patch them properly. After they are patched, I leave them for 24 hours. I then inflate them, and leave them for another 24 hours to check for any air loss. When I verify there is no loss, I deflate them, roll them up, and put them in the pile of spare tubes.

When done like this, I have never had a patched tube leak at the patch.

I understand the cost/benefit of using new tubes, especially if you buy them in bulk and on sale, but it's just a waste to toss them. Most of the guys I ride with only use new tubes when they flat, and give me their punctured tubes. I patch them and am more than happy to pass out patched tubes to riders in need at no charge, sometimes even to the guys who gave me the tubes in the first place

To each their own I guess, but take the time to learn how to patch, you never know when that ride will come along where the number of flats you get is the amount of spare tubes you have + 1