Again, trip itineraries are not unique to winter camping. Itineraries are one of your most important safety techniques. The itinerary is left with responsible people who will act according its instructions. It should contain your route location information, dates and details for ingress and egress, your visual appearance for airborne searches, and overdue buffers, i.e. if you are not out by a certain day, it provides X number of days to be late coming out before launching a rescue. Winter trekking is slow, and weather events like blizzards could pin you down for a day or two, so its always possible to fall behind schedule while being perfectly safe. You may wish to pack extra food for longer tougher trips going further in.
The itinerary should be a stand-alone document so that a friend or family member who is worried and may not know anything about winter trekking or the locations, can hand it to authorities who can interpret it easily and find you. For a difficult trek, i.e. an expedition, you should file with your provincial or state police force, and fully brief them on the details.