I live in Brooklyn, work in midtown Manhattan and get motion sick if I read on the subway, so I have a lot of time to look around while I ride the train every day. As you might imagine, I tend to look at people's bags, and in the year I've been doing my current commute, I've noticed that the Madewell Transport Tote has a surprisingly monopolistic presence on the arms of the borough's population of young women.
A seemingly ever-growing portion of Brooklyn has transmogrified into a home for creative young adults (ahem, *points at self*) of various types, first because it was relatively affordable, compared to Manhattan, and now because all of your friends live there so you might as well move. Young creative types often don't make a lot of money, unfortunately, and Brooklyn is now basically as expensive as Manhattan, so that means a huge pool of style-conscious women need an affordable, functional, nice-looking leather bag for their schleps to and from work, often in Manhattan.
That's where the ingeniously simple Transport Tote comes in. It's big and roomy, but its basic construction keeps it lightweight. The bags are rendered entirely in solid-colored leather, which keeps them fairly anonymous (unless you're looking), but still polished enough for use in most offices. Although I don't own one, they also seem durable--one of my closest friends carries hers constantly and has had it at least as long as I've known her.
Perhaps most importantly, the bags are also within reach for women just starting out in office jobs: you can pick one up in a variety of colors for $168 via Madewell, Nordstrom or Shopbop. If you want a zip-top version with a dedicated shoulder strap, it'll only run you $188 via Madewell or Shopbop.