Longchamp Le Pliage. I've had my custom nylon travel bag since last autumn and I seem to be carrying it almost every time I travel or need to carry alot. I've taken it on a work trip where I needed both work attire for the meetings and ankle boots and other ruffles for dinner and night out. All fit perfectly and I didn't need a separate handbag.
A Large nylon or Néo LP would probably be a great size for you- I do love my LP Cuir Medium as well, and if you pack minimally, it might fit all your necessities. If not, there's a Large size as well.
All Le Pliages are light as a feather, durable and the selection is endless.