I use a normal Samsonite laptop bag. Since i don't need a laptop the front compartment has enough space for my headset and other stuff like food for the day. The back compartment has enough space for passport, license, medical and a pouch for the iPad, as well as enough for the paperwork of the day (usually just the briefing sheet).
And i like that it opens up top so i can easily reach inside from my seat.
Just went into the next store and got the cheapest one that had the features i wanted, ended up with something like
this.