I'm not sure about this idea, both because things that could be replaced by a free web site or cheap mobile app should be, imho, but also because travelers don'

I'm not sure about this idea, both because things that could be replaced by a free web site or cheap mobile app should be, imho, but also because travelers don't want more stuff to carry, and people in general (not just travelers) want fewer, not more, paper products these days. You might have an interesting starting point here not for a physical product, but for a mobile app or web site that does a bit more than a deck of cards could do. Maybe a site or app for crowdsourced location-specific activity ideas, for example.