I’ve no experience of run-flats, but tyres are part of the suspension. [some] People say they don’t like them even when they come on cars designed for them, which would be enough to put me off using them on a car that isn’t.
I carry an additional gloop kit, a tyre string kit, and a jack, all of which I added before a trip to the Italian lakes. For nails and screws, plugging is fine even though it is not a permanent repair according to the British Standard and certainly good enough IMO until you can reach a tyre shop (this is not advice, just my opinion!). If the tyre is unrepairable I would have an option to remove the wheel for me or somebody else to take it for repair if recovery was not at hand.
A standard MX-5 jack was about £20 on ebay and clamps into the space provided in the offside rear wing behind the boot lining. The odd one is sold with the T-bolt to hold it in.
Of course 3 repair options and a jack aren’t as foolproof as a proper spare, but the fact is that when it would be of most benefit (halfway up an Alp on a Sunday evening) you probably won’t have had room for it anyway.
Which reminds me, take a head torch.