Thanks for the repllies so far.
I chose the Civita for the size. Some airlines are limiting the size of personal items and the Civita, if not fully packed, shouldn't be a problem meeting the limits.
I have a bag bungee, as shown in the Amazon link, an add-a-bag strap, and bungee cords. I just want the ease of being to slide it on and off the roller bag without having to use something else.
I think I may have found another bag to use instead. (This will not be my daybag but then neither was the Civita as I don't like lugging backpacks.)
Lite Gear RFID City Tote.
Just slightly smaller, same basic design, includes the roller strap.
But I'm still open to more ideas for adding a strap to a Civita day bag.