I always use Rema Tip-Top patches and glue.
Even during the times of greatest crises and scarcity, I've always been able to have and keep a small stock of those.
When I use that (along with Schwalbe or Continental tubes), I'm certain enough that any problems are down to my poor work/preparation, not some other reason (I usually do a good job and very, very rarely see problems with my patching jobs).

Apart from that:
I make sure my tubes are not kept in direct sunlight or near some heating elements.
Likewise, I keep tubes in a plastic bag, to prevent any extra oxidation.
This way, I've been able to use 3 tubes (2 on the bike, one spare) in rotation (spare tube goes on a bike, the punctured tube gets patched and becomes a spare tube) for a decade, on a regular basis.