I've been using the
ThinkTank Skin 50 for a M8.2 w/ either 28/2.8 or 50/2 attached + a 90 tele-elmarit on the bottom with either the 28 or 50 in a leica leather case on top of the 90 tele-elmarit. It fits everything perfectly and there's a pocket for battery/SD cards.
The 90 tele-elmarit takes up next to no room on the bottom of the bag but if you were to leave the leica leather case out, it would be just a touch loose. The bag also comes with a rain cover which is stored in a small zippered pocket on the bottom of the bag which serves as some padding/protection.
The only thing you need to add to make this a small shoulder bag is a shoulder strap of your choice. I had a spare thinktank strap kicking around so I use that to turn this pouch into a very compact shoulder bag but any strap will work as long as you can hook them to the two attachment loops on top of the bag.
The bag itself has a elastic draw cord that can be used to close the main compartment and the flap has velcro which can be covered so that the vecro is not being used. Or you can partially cover the velcro so that it's not has hard to open the flap.
All in all, it's a great little bag for just strolling around. It's well made, super light (weighs 5 ounces or less than 150g), cheap and doesn't attract attention.