I don't normally have to bring work stuff home but when I do, or when I have meetings outside of the office and I have documents with me, I use this black N/S Le Pliage Longchamp Cabas as my extra bag. It's lightweight and since it is black, it still looks professional IMO.
I also have the LP Cabas and also a document briefcase from the same line, both in black, For less-than-ultra-professional meetings or other occasions I usually take them, but for more formal occasions I use my Longchamp Roseau which is SO chic it's not even sane anymore.