I highly recommend a warm bag, or heater body suit. I got my wife a warm bag a couple years ago and she hasn't been cold since. I used it twice this year, both times I left my "warm layers" home, went in dressed as I would for a 40-50 degree day.
- first day was 20 degrees and 20 mph wind. Sat for hours and was toasty warm. Actually thought the weather guys were wrong on temperature, until I got out of it and walked 15 minutes back to truck and froze solid.
- this past weekend, when I left home at 5:15, it was 7 degrees. High for the day was supposed to be around 20. I sat from just before light to 10 AM, about 4 hours. It was COLD. but I was not. I won't say I was warm, but I was comfortable.
Allows you to layer lightly for the walk in, and then get in the warm bag. Now add to this that I don't actually fit in my wifes warm bag, it comes up to my arm pits, so I put my jacket on, but didn't zip it. Had a WARM hat on that covered my neck. I was VERY comfy on a day I normally would have been frozen solid depsite layers.