You can put some weight in the trunk (such as with sand bags), but your car has a 50/50 weight distribution already and I just do not think it helps much. Do you at least have all-season tires on your car?
What you might want to have in your trunk is two carpet floormats, a small shovel, and maybe some salt. If you do get stuck, these items will come in handy. Naturally, your best bet is to get a set of snow tires for the winter months...then you're pretty much guaranteed not to get stuck on the streets, assuming they are well-maintained during snow storms.