When I'm out all day doing a 20 mile circuit, it's really annoying if I get a puncture. So I do everything I can to avoid this.
First of all, Kevlar reinforced tires.
From Asda folding tires at £11.48 or the very fine Schwalbe Black Jack from Tesco for £12.42. I prefer the Schwalbe, but I carry a folding tire in the car, it takes a lot less space than the Schwalbe.
Next, the inner tube. Normal inner tubes are very thin, but you can get thick-walled inner tubes that are much more puncture resistant. And they're cheap if you get them from JeJamesCycles here at only £1.75 each. Again, I carry a spare in the car.
Between the tire and the inner tube, I like to put a gel liner, "Slime" brand or "Dr SLudge" or "Weldtite". Dr Sludge from Ebay, £10.99 for a pair. Make sure you get the correct width, then you cut it to length. The trick to installing it, is put on one side of the tire, then the inner tube, slightly inflated, then thread the gel tape between the tire and the tube. Then put on the other side of the tire, then inflate.
This has saved my bacon at least twice, apart from any thorn prevention. I've had tires worn so badly that they weren't just bald, they were completely worn through in one place and I could see the gel liner. But I was still able to get home, very carefully!
You wind up with a wheel that's quite a bit heavier than with a light tube and no gel, and because all the weight is round the rim, a much higher angular inertia, but certainly for me it's worth the puncture resistance that this gives me.
And I still carry a puncture repair kit, pump, spare inner tube and spanners.