The wrapped sausages - I prep them and freeze them in the disposable foil trays in which I will bake them.
The meat - I stuff, truss and weigh it, then wrap it in foil and write the weight on before I freeze it. We don't have turkey, but I expect you could still do it with turkey.
All the roast roots can be par-boiled, greased, seasoned and frozen in bags. Freeze them spread out so that they don't stick to each other, though you can shake them down to the bottom of the bag for compact storage once they're frozen.
We make an obscene number of mince pies, then freeze them in bags of about 15.
Cake for the trifle can be made ahead and frozen. Can even be jammed and sherries, if your trifle bowl can be spared for the freezer.
Christmas pudding and Christmas cake don't need to be frozen. In fact they taste better if made well ahead of time.
We always have gingerbread, and I managed this year to remember to make the dough and freeze it. Unfortunately it seems to have disappeared into the gaping maw of the freezer, and I don't think I can be bothered to take everything out to search for it!