As the sort of traveler who never goes anywhere with more than a carryon, my favorite bag for years has been the Briggs & Riley Baseline tote. One side unzips and slides right over a rollaboard handle. It holds anything not in my carryon, basically, but still is passable as a purse while at my destination. Plus it has a lifetime guarantee. I still love it as much as when we first met a decade ago.
http://www.briggs-riley.com/category...line&cat=totes