Similarly, I recall back in the 60's wandering the Seattle waterfront area carrying an M2 with 35mm above a Spotmatic with 85mm with straps adjusted accordingly. Quick into action!I kind of did that once, only with an F2S, and a Yashica GX...
I lengthened the neck strap of the Nikon, and shortened the one on the Yashica so they wouldn't hit each other. The VUWS was in a jacket pocket, and the TZ-3 in my camera bag, reserved for when the film ran out.
But I had the same B&W film in both cameras, as the point was to have two focal lengths immediately available. Besides, I have found it very difficult to see both color and B&W photo opportunities at the same time. I'm either in a B&W seeing mode, or a color seeing mode. Just a personal handicap I guess...