I've thought about that one a lot, since where I live it's the main "survival challenge".
In Texas, we don't worry about insulation, firewood, keeping warm without any natural gas/electricity -- it's very easy to do.
We don't have to worry as much about preserving food for the winter, since it only lasts a few weeks here, and there are some crops that only grow during the winter! We can literally grow SOME kind of crop year-round here.
HOWEVER --
Water is another issue. We don't have a lot of rivers, ponds, and streams around here, so unless you're in the country and have a well dug, you don't have a good supply of water.
I think all a person can do is get a bunch of gallon jugs and fill them -- as long as you have some space in your backyard/shed/basement/attic/storage room. Supplement that with nice, brand-new 32 packs of bottled watter from a wholesale outlet like SAM's club.
Also -- for a more permanent solution -- I'd recommend getting gutters installed on your house, and get some rain barrels to collect the water. At least then you'll be fine whenever it rains. (Though in Texas there are long dry spells during the summer)
To purify water easily and cheaply, make sure you own AT LEAST 5-7 gallons of bleach. Wherever you get water from, no matter how bad it is, if you can filter the sediment out and put a teaspoon of bleach in it, it will be drinkable. You can even get rid of the "bleach smell" by pouring it from one glass into another, repeatedly.
Bleach is a universal purifier and cleaner, and it's very cheap. It's a very important "prep" item. Considering it makes water drinkable, and you can die within a couple days without water -- I'd say it's at the top of the list.
Survivalists often recommend having some instant tea, Tang, Kool-aid, etc. on hand to flavor your water, so it will taste a bit better, especially for the kids.
Matthew