For car prep I throw in my army issue sleeping bag (the newer kind with the goretex cover), snowshovel, and ice scraper. Thats it. I have a cool little seat cover that has MOLLE attachments all over the back, and allows me to keep an alcohol stove, food, some clothing, and necessary survival gear there all year long. Other than changing out the fuel in the stove every few months, and rotating the food, nothing else really needs to be done.
I also live in an apartment complex, so I usually keep a few gallons of water that I store in 1 quart jugs, handy, just in case the pipes freeze. I also put plastic on the windows-thats about it!