Your 6D setup is perfect for europe. I took nearly the same setup a year ago and was glad I did.
I agree. I'm a big fan of the ultrawide zoom. The 16-35 is about my favorite lens. For walk around, it's also hard to beat the 24-105 or the 24-70. Personally, I carry the following...
5D3 or 6D w/ 16-35-f/2.8 or f/4 (Depending on low light or sharpness need)
Small Flash with diffuser (SunPak SD2000 or 270EX II)
24-70-f/2.8 or 24-105 (Depending on primary need, reach or low light)
15mm f/2.8 FishEye (super cool fun lens, esp for interior shots and "all over around" shots w/ people in the foreground
CPL Filter, extra batteries, extra mem cards.
I have a small pouch I use for the batteries + mem cards for my pocket.
The 2 lenses not on the camera fit nicely stacked in a LowePro Lens Case 2 with a foam divider.
I put everything including a rain jacket, and other travel items in a simple inexpensive day pack and I carry the camera on a simple BosStrap shoulder type hip side carry sling strap.
If I need a fast prime lens, I take the 50-f/1.4, 50-f/1.8 or the 28-f/1.8. (This could be easily substituted in the Lens Case 2 with the FishEye if the FishEye isn't your thing.)
This whole arrangement is fast and light and will easily go through security checkpoints, subways, crowds, etc and it doesn't scream photographer or expensive gear. If I want to be even less conspicuous, I wear the jacket over everything including the camera on the side and the backpack and it stays dry or is simply covered up.
As for the EOS M, meh... it's a bit heavy and bulky. Not sure why you need it. If I take a backup camera, it is usually a little S120. That way, if I end up going to a formal function or something and I still want a camera, I'm covered. I can also easily hand the S120 to a friend, wife or whoever and they can use it easily. It weighs nothing and is very small but still takes decent snapshots and shoots RAW so in Post I can later see how much noise the little sensor added. LOL!