Fiction. I was called to a dedicated LPG Commodore recently with a flat tyre. It didn't have a spare but it did have a can of goop and a compressor. Problem was it went flat at 110kph on the freeway and by the time he got into the service lane the tyre was trashed. The goop would not of fixed it and I doubt whether a field of freshly slashed grass would have fixed the side wall.
Fact
its fact it was on bush mechanics years ago.
much to my surprize they jammed in as much grass as they could poking it in with sticks. after they broke the bead, side walls where still ok though.
they got far enough to get it repaired, maybe not high speed though.