It seems silly, but the best saddle bag I have was a spur of the moment hack when I was in a hurry. It is more convenient, holds what I want but cinches up well, and looks fine. As far as I'm concerned, perfect for a saddle bag.
It could probably hold twice this if I wanted:
The bag is nothing more than one of those round CD cases with a velcro strap pushed through in back, and a toe clip strap
On the bike I just loosen the strap and unzip from the top.