This is excellent advice, I should have mentioned it . With thorns or cactus spines, (you get a lot of these in England? ) you can run your hand through the tire and realize you've got 3 or 4 more hidden spines you didn't pull out. This is how Baja riders have 8 flat days Been there, done that.

Slime is water soluble and cleans up in two minutes. With a tube and Slime, there IS not a mess unless the tube is shredded. Rare. When I hear this stuff it makes me realize folk have never actually used Slime before, or are using the old style sticky Fix-A-Flat foam crap they used to sell. Slime is totally different, not a foam, not sticky and it works! It is not new, we've been using it for over 10 years here.

Gimmick? Come to California and meet some real desert racers. It's not a gimmick. We learn a lot from racing and racers. Pick up the useful stuff, let the rest go. 21" tubes have worked for thousands of riders for decades. Not just racers, just normal dual sport guys too.

I said use a 21" tube "In a Pinch". This means if you are out of rear tubes, use a 21". I carry both sizes. BTW, Racers don't stop to change a tire, they just ride it flat round to the pitts, then the crew just fit a new wheel. Running a 21" tube will never cause damage to a tire, it might go flat, little else would happen unless you rider is dump enough to ride the flat across Mongolia.

On a rare occasion a 21" may fold or crease funny and get flatted, but I've not seen this happen .... in about 30 years. A motorcycle is not an outfit. On an outfit you can haul spare wheels/tires, jacks, Beer and G clamps. Not so much on a bike!