Patagonia.com has the 25 liter and 32 liter black hole backpacks on sale for the unpopular colors. The 25 Liter looks like a good underseat bag for minimalist packers or for a personal extra “just in case” bag. Would make a good trail daypack as well for hiking.
I don’t personally own either of these packs. But, I do have a patagonia pack. My eye is on the 25 liter one - but, not in a sale color. (Good thing - keeps me from buying another bag.)