CX / Gravel: Not only a spare: It is not only a savior in need, but can perfectly well also be used on a daily basis as it is still as robust as a standard butyl tube. It is developed to fit in any small pocket.
 
The 35 grams lightweight S-Tubo-CX/Gravel-All is the ideal spare tube for all 700C and 650B tires with a tyre width from 32 - 50mm due to its very small packed size. Leftovers of tubeless liquids do not do any harm to it.