I commute 55 miles (each way) by train Mon-Fri. I have, virtually always, an old, black Billingham Hadley with one M Body, 35mm and 90mm Summicrons + spare roll of film (+ phone, glasses case, etc).
Last weekend, the same bag contained my Hasselblad 503cx, 80mm f2.8 and 50mm f4 + 3 rolls of 120 and all my other bits and bobs. For those familiar with Doctor Who, I call this bag my "Tardis" as it is capable of carrying much more inside than its external appearance suggests.
There are numerous other bags in my cupboard, some considerably larger than the Tardis but I've never found a better, more protective, ergonomic and durable bag than those made by Billingham. But I can only speak for myself, of course....
I have the Billingham f/2.8 for larger kits and the Hadley Digital for when it's one camera and one (possibly two) lenses. It's in between where I look for something else.