I have not had the pleasure of camping in the snow. It does get cold here in Tennessee, but not to the extreme that Canada gets. We get some snow once in awhile, but it usually only last a couple of days or so. If it isn't going to be above freezing during the day then I usually won't go. I expect below freezing at night, so I concentrate more on my sleep system. I will take an insulated sleeping mat, sleeping bag rated for colder then expected, military surplus wool blanket, and a felt sleeping bag liner. I will lay wool blanket over sleeping pad and then sleeping bag on top of it. If I feel to constricted in the bag I will unzip part way, and cover with felt bag liner that I unzip to make a blanket. Also if I need to get up in middle of night for whatever reason, I can wrap up in the felt liner like a blanket. I pay alot of attention to what I am sleeping on to keep my back and sides warm. I wear as little as possible in my sleeping bag usually under clothes and socks, and if I have room, I put the clothes that I will be putting on in the morning in the foot of my bag to keep them warm.
As Northern Dancer has stated in the post Dare Devil Camping, dress like an onion layer your clothing.
