I carry a spare tube, a couple square inches of an old tire in case of a slash, and a self-sticking patch kit. I find it's fastest to slap a patch on, since I can just lever the tire out still on the bike, swipe out the sharp stuff, stick on a patch, and reinflate. But the spare tube is nice to have around; if it's raining or something I may not be able to get a patch to stick.

When I get home, I put a REAL patch on (rubber, applied with rubber cement, clamped until set). I have tubes with 5 patches on them. The patch is stronger than the rest of the tube if done right.

If I ever get a tube that's got 10 patches on it, I might give it the honor of meeting a pair of scissors and becoming my next few dozen patches.

Glue does not "wear out" because when properly applied with rubber cement, the rubber is welded together. You can't even tear them apart regardless of the age of the patch; you'll rip the whole tube apart first (I've tried).

I think rubber cement is all the same and hasn't changed for 100+ years. I use the stuff from the office supply store, $1.50 for a can of Elmer's. I use it even to plug holes in my car tire, and have run tires plugged using that stuff for 10's of thousands of miles on my car.

I ride largely due to environmentalism, so I'm sure not going to throw out a tube because it's got a tiny hole in it.