"But a survival knife is, to drag out an old line, is the one you have with you when it all goes south."

True. If you take it for planned purposes it is more likely to be a 'camp knife' or similar.

For me, it's a tiny SAK on my key ring, plus a sub 3" bladed slippie (UKPK, NRA stockman or Trevor Ablett Farmer)

I'm not an outdoorsman, but I suspect that 99% of any genuine crises I face will need to be tackled with the contents of my pockets at that point.