UrMajestywrote a review of Patagonia Black Hole Mini Messenger Bag - 732 cu in on February 27, 2017
Familiarity: I've used it several times
I have virtually every size of Black Hole bag available. I justified this purchase because I recently had a flight on Spirit Airlines, and apparently you are allowed one purse or murse for free. I ended up using this murse the whole trip instead of my 32L black hole backpack as it fit everything you needed for a day.
As a side note; there were many people with much larger (personal items) on my Spirit airlines flight, and none of the airline employees said anything.
You should probably purchase this anyways just to be safe ;)