For the batteries, I would consider storing the batteries somewhere warm (if your jacket has one, an inside pocket would probably be good) and then only popping them into your camera when you're going to start shooting. I haven't tested this out, but even though the battery would probably cool off quickly enough, you could still get some extra shots out of it.
I think the hint about sealing the gear in a plastic bag before going to a warmer environment is a useful one. I've never really done that.. I just tucked my camera into my jacket before I went indoors, and left it in there once I was inside until it warmed up enough. It worked well enough. The only time I've had serious condensation was when I was trying to shoot star trails at night. My black camera cooled down quickly (a little known flip side to the well known fact that black things absorb heat from light is that black things also radiate heat and so cool down faster as well) and I ended up only getting maybe 15 minutes of star trails until the pictures were blurred out by water condensing on the lens.
My one other uncertain suggestion is that you might want to let the camera cool down adequately before taking pictures. I'm not certain of this, but I know that it's standard practice in astronomy to let your telescope cool down to the ambient temperature before using it. I did some winter shooting last winter, and it seemed that when I first took out my camera, after keeping it warm in my jacket, and starting shooting the winter scenes (I was shooting animals in the zoo with snow on the ground). I got too many less than sharp pictures, especially the first shots I took when I first took the camera out. I can only guess that my lens was still in the process of cooling down at first so it wasn't producing optimal images.
Mind you I was using a long telephoto lens, if you won't be using as large a lens it probably won't take you as long to cool your camera down.