Just been through this myself. Bought a new car, and it had no spare....just the little compressor and the "goo". We do a reasonable amount of country driving (I'm in Australia, big distances between major cities) and I figured that "goo" won't be much use if I have a blowout or a damaged tyre, so went the expensive way and bought a new full-size wheel and tyre for a spare.
Couldn't buy one from the dealer, but luckily could easily get one from a local tyre/wheel retailer. Not cheap, but I now have peace of mind.
Are skinny pin-drive wheels available for our cars?
Cheers, and good luck with the "goo"
Glen