When I was away from home for a while, I took my Bronica outfit and about half my Nikon gear and left them at the place I was staying; I would bring one or the other depending on whether I was photographing people. In other words, I don't really bring multiple formats with me, unless you count the P&S in my pocket. I used to pack my 35mm gear and my TLR and my 645 rangefinder, but gave that up a while back.
Since you like chromes, I would just leave the Nikon at home and shoot chromes and B&W in the 6x6.
As for gear, I have a number of bags, and my favorite for working out of remains a small shoulder bag (I have a LowePro Nova 4 that is just about the right size) and my favorite for carrying is a backpack (I have a LowePro PhotoTrekker which now houses my 4x5, and it's fine but big, and a little Tamrac that's okay but too small). The advice I was given was "go to the store with your gear, stick it in bags until you find one you're happy with, buy that one".