Not having a full sized spare, or not having one at all, in my view, is madness. When I started driving back in the sixties, it was absolutely necessary to have a proper spare. I also drove HGV's for 20 years, on the continent, and there is no way we would leave our yard without having two or three [depending on the spare wheel carriers on the tractor and trailer] spare wheels.
It always amazed me how many people can't, or won't, change a flat tyre. I see people sitting on the hard shoulder of a motorway waiting for Green Flag to arrive, to change a wheel. I would want to get off the motorway as quickly as possibly, and there is no way I would be sitting around waiting for a breakdown van.
People are too lazy, these days, to bother checking their spare wheel to see if it is at the correct pressure, and it is a case of "out of sight, out of mind". Having been brought up in the days of proper driving, and car ownership, I have no sympathy for some-one sitting on the side of the road with a flat tyre, and who couldn't be bothered to get out, themselves, and change it.
The other interesting issue is that of different sized tyres on a car. I really don't understand companies, and people fitting, for example 8 x16 on the front of a W126, and 9 x 16 on the rear. If you fit an 8 x 16 in place of the 9 x 16 then the car will handle most oddly, and may in fact be illegal.
I fitted 8 x 16's all round on my W126, and I went to great lengths to have 5 wheel rims the same. The 8 inch rim is obviously quite a bit bigger than the original 6.5 inch Mexican Hat spare, but it still fits the spare wheel well in the boot, although it is a bit tight. It is also higher, and what it did was to get a friend, who is a carpenter, to cut a new wooden board to cover the spare, using the boot carpet as a template, and then fitting small wooden spacers under the board, to sit on the top of the wheel well chassis rails.
This ensures that the boot "floor" is as strong as it was originally, and can't bend at the edges.
As the 8x 16's sit out at the front, but not at the rear, I fitted 10mm hubcentric spacers, which I suspect give the same width of track as if I had fitted 9 x 16 rims. By fitting the spacers the look of the car is hugely improved, and looks correctly balanced. And I have to have only the same sized spare wheel to replace any of those on the car.
I know that one can use the emergency inflation cans, but I did hear that the tyre fitters don't like repairing tyres with a filling of gloopy glue. I don't have experience of these emergency cans, but I know that I would much prefer a proper spare wheel than a pressurized can.
I have no issue about buying a full sized spare wheel where necessary, and I had to do this for my 2009 Jag XJR, which only had a space saver in the boot. The same thing happened with my E220, again which had a space saver wheel. In both cases I bought an original wheel on E-bay, and had the comparable tyre to the car fitted.
parkman