I have to admit that I don't always trust patches on bike tubes. Many things can go wrong with the process. A seam in the tube can interfere with adhesion of the patch, or the glue can be too old and not hold. Or, user-error can come into play.
So, I tend to replace the tube with a spare, and patch the tube which went flat. I then put the patched tube in my bag, just in case...
But, I occasionally get in a mood where I don't want to waste tubes, and I start patching them instead of replacing the,
Once, I had ridden the same tubes, all summer long, and really didn't keep up with how many flats I'd had. When I replaced the rear tire, I pulled the tube out and was a little surprised: 18 patches!
Hell, I should have kept that tube, forever. It was more patch than tube, and probably more thorn-resistant than any commercially-available tube.