OK, this may be a stupid question but I'm gonna ask it nonetheless:
Let's say I replace my runflats with a set of, say, Eagle F1's and carry a can of goo etc. Then one day I'm driving along and I get a puncture - no problem; I use the goo to re-inflate the tyre and drive to a tyre dealer.
When I get there, the tyre turns out to be non-repairable and they don't have any F1's in stock. Obviously they can order one but that'll take a couple of days, so I'm left with the choice of having the car unusable for a couple of days or letting them whack whatever alternative they have in stock on the wheel while I wait for my new F1 to arrive (and thus end up paying for 2 tyres and 2 lots of labour) - assuming that I can't live with a mis-matched set of tyres

.
The alternative is to buy 5 tyres initially, keeping the spare in the shed "just in case", which seems a little wasteful too.
I guess this is a side-effect of not having a spare or emergency wheel to fall back on. I was just wondering how everyone else approches this problem...