My total kit is an M3 and an M5; 35 1.2 CV Nokton, 35 2.8 goggled Summaron, DR Cron 50, 50 3.5 CV LTM Heliar, 90 2.8 thin Tele-Elmarit, 135 2.8 Elmarit. And a 25 CV LTM snapshot skopar.
The wides are used with the M5, for obvious reasons, except the goggled one; the 90/135 usually on the M3 but far from always. The fifties go on either camera. I really have to get a 25mm external viewfinder one of these days by the way! (Sometimes I take my Barnack out for a walk too, but then it's with a fifty, a Summar or an Industar or the Heliar; I don't normally use the two first ones on an M.)
I tend to have one lens on camera and one in my pocket, except with the 135 which is frankly too big to be easily combined with anything else. Typically I'll carry the snapshot skopar and a fifty, or a thirty-five and the ninety.