@mjray for a long time I read your name as Mr Jay. I'm not dyslexic and I had no intention of insulting you. In fact I only discovered my error when tagging you in a post and the automatic user lookup thingy failed to locate @mrjay.
But back on topic, sort of...
I have been wondering, just how adaptable are inner tubes? I have given old style (27 x 1 1/4 or similar) to a friend running modern (700x25 or similar) as a get you home measure which worked ok. But in extremis, how far could you go? I stopped to help a MTBer with a puncture and no spare tube. I gave him some patches, but I wonder, would a 700x28 tube have served to get him home? After all, inner tubes are very very stretchy. Offhand I have no idea what size his wheels or tyres were. They were big and knobbly.