First and foremost, the bunny must be protected from wind. Wind can be quite bitter, and we must remember that for our rabbit's health. Although the rabbits don't need protection from the cold, they absolutely must be protected from rain and snow. It is not only because of the various sicknesses that can occur (pneumonia, snuffles), but with angora rabbits rain or snow can completely destroy their wool. When their wool gets wet, it mats, and then the body heat from the rabbits can totally felt the wool, which can make the rabbit really uncomfortable.
During the winter, around the Sierras, sometimes the semi-trucks carrying hay and feed can't make it over Donner Pass. This can be pretty serious because you can't just suddenly switch the rabbit's feed to something else; rapid changes in feed can be fatal. And of course, you need hay.
When temperatures drop below freezing, water bottles can freeze and even burst. For a thirsty bunny you want to get it water as soon as possible, so it isn't such a bad idea to store one or two extra water bottles. That way the bunnies don't have to wait for you to thaw their water bottle inside the house. On bitter nights it can even be a good idea to get up at midnight to change bottles. Rabbits won't eat if they can't drink. It can also cause kidney problems later in their life if they go long periods without water.
It is a good idea to buy extra food for those days when the semi doesn't make it. It causes a lot less stress when you don't need to worry about feeding your rabbits. I would recommend three extra bags of rabbit feed (for my ten rabbits). It isn't likely that the semi would actually take that long, but you don't want to be going to the store once a week asking if they have food. People who didn't store food before winter can get stressed when they go to the feed store and there is no feed. They can then end up buying a bit because they don't want that to happen again. This happens with multiple breeders. Even though the semi eventually made it, it can be bought out quickly.
In areas that experience freezing temperatures