If form and content should follow function, then a kit's function offers guidance. All of my kits evolve to address the functional categories: first aid, shelter, water, food, fire, navigation, communication, hygiene, and morale.

For winter vehicle travel, I know I will have my EDC, PFAK, PSK, and BOB already. My car kit amplifies each functional category with more robust and abundant gear, plus vehicle maintenance and vehicle self-rescue items.

If I have a chance to encounter extreme conditions, then I go through each functional category and try to include whatever might be handy if I had to survive a few days of extreme conditions.

To address extreme cold, for example, I would follow the old adage that the best way to get warm is to stay warm - more and warmer clothing layers, more and higher caloric foods, and full vehicle gas tank. Personally I find I need more hydration in very cold conditions, so I would beef up my water supply, too.

If snow was possible, then snow chains and possibly a snow shovel would be added. If snow was certain, then I would consider some rock salt, sand, and perhaps a few yards of tire traction mat. My vehicle is not suited to off-road snow travel.