[Cockbrand]

Lately, many Presta tubes come with valve nuts that fit Schrader valve holes. The nuts look similar to this: https://m.media-amazon.com/images/I/612j5EAmLXL._AC_UF1000,1...

So there's not necessarily a need to carry tubes with both valve types.

[schoen]

Oh, I think I've seen one of those! Cool, that could definitely help for emergencies.