I often go out shooting in the middle of snowstorms, so here are some things I can suggest you taking.
First, an extra darkcloth. If your shooting in the snow, usually one will get wet or you will use the other for covering the camera. You can also take a trashbag or thick fabric to throw over the camera bellows, and leave the lens barly sticking out to focus, and make the exposure.
I have always used older lens/shutters...and they ALWAYS stick open on me! This past year, I started using new shutters (Copal) and I have yet to have it stick open.
I put that "No Fog" stuff that they use in snorkle/scuba masks...on my ground glass. This stops it from getting fogged up really bad.
A good lens hood is always a smart thing to have in blowing snow ect. It keeps stuff off the shutter and lens, unless its blowing into the camera of course.
Also, if its snowing when you pull out your darkslide, COVER IT RIGHT AWAY. You do not want snowflakes landing on your darkslide, then it being put back into the film holder and getting water spots on your film when they melt!
Have fun shooting during the winter and take advantage of it! It is my favorite time of the year to photography and their is nothing more exciting then hiking thru waist deep snow with an 8x10 over your sholder!
Ryan McIntosh