Looks like if you are winter camping as in backpacking, a couple of things should be considered:
A.) While accidents can happen anywhere, anytime, as discussed in SAR threads, the margin of error in winter is thin and the colder it is, the thinner the margin. Gear that holds liquids or fuel needs to be fool proof, you need to know your stove and if needed fix it in the field, same with snowshoes or crampons if your destination means you can't limp back (100 Mile Wilderness in Winter for example and Western and AK or the like)
B) you are really serious about this - meaning, you should consider laying down serious cash and get a down bag or a porter or a sled (steep trails and sleds, are you part yak?)
The hard part as we learn is how to make the transition from 3 to 4 season feasible financially (Knowing that Daytrip is past this but others in the future may find useful) Can I extend my three season 20 degree bag with an overbag or wool blanket or wearing oodles of clothes without compressing loft? (Down booties a piece of gear that is always good) Starting the longer trips in less severe climate like driving south for a few days in VA where it's unlikely you will find weather to overwhelm your 20 degree bag, extra clothing and other "winter starter" gear.
As I believe we mostly do here, planning your trip well and being willing to change it if looks dangerous. (A VA winter trip might, depending on location, be more likely to have snowpack that melts in a 35 degree rain that causes flooding and makes streams you crossed on the way in impassable instead of a -25 night. (Like we had here at Christmas,) While in January here, for now, we are more likely to have a -30 night than that type of rain in northern NH, VT, ADK or ME. While possible, we are more likely to see snowpack melt in a large rain storm in Nov, Dec. March and April. (Yes we have snow in October it's usually not enough to add a significant total to a rain event & by May, usually only snow is above 3000 or 3500 feet. (It might still make unbridged mountain streams tough to cross or in places with deep drifting, say the Great Gulf or Panther Gorge)
I probably will not get to the winter White Mountain backpacking level as I'd likely be solo. Through Scouts I inherited an old Mountain Hardware Polorguard, made in the USA synthetic bag that I was able to determine it was likely a -20 or more bag and was lightly used, and dates to the 1995-2005 period . I can get it in a garbage and compress it so I can tie some rope around the top. It's perfect for winter car camping but would require a rocket scientist to make it fit a backpack you would like to carry. (I NEED A YAK)