Thanks. The Skypack is the kind of thing I'm looking for. I did click on the brand's name to see if they had anything even smaller. That foldable bag holds more than my main luggage. I found the following linked to from the above on Amazon:
and:
I would think that even the 25L would be fine for my purposes, but I would prefer a brand I'd been recommended than a random unknown brand.
@antichef Is there a link to your thread on the topic?