Hand warmers. Several handwarmers. I have an elstic wrap that holds large warmers and i wrap them around my kidneys.

I wear a thermal union suit. 200gr fleece pants and bibs. This keeps the core warm without a big coat.

Top is generally a fleece wind proof jacket. This allows me to stay warm and still maintain flexibility to shoot.

I have tried wearing my parka and several layers and even with an arm guard i cannot shoot past 20yds accurately. This way i keep most of the core warm and still have it not too thick in the arms.