We have just started doing a few things without costing too much or drawing attention to ourselves.

First we gave our basement a good cleaning and bought some shelves.  Whenever I go shopping I pick up a few extra canned goods and some people give us things.  I take them to the basement where it is about 65 degrees.  I have cans of beans and corn, several large cans of peanut butter, several boxes of pasta.  Those really big cans of crisco can be used for candles.  Put a string or wick in one and it will burn for 30 to 40 days.  

We are currently trying to work out a water supply and some way of getting rid of bodily waste in case we need to stay in our basement for a time.  

We have also started collecting anti-biotics.  Even expired anti-biotics can be used if necessary.  

Also, we have started collecting and printing out manuals for building and repairing things.  

Also, every time I take my children to the dentist, I ask for an extra toothbrush and toothpaste sample.

If you have children, you might want to collect extra packages of diapers whether disposable or cloth.

You can also buy large metal cans to store sugar and flour for long periods of time.

Also whiskey, wine, and beer might be useful to keep for consuming and sterilizing.  

We have a camping toilet for waste containment that we bought in the local Wal-Mart type of store.  (We are "luxury" campers.  I have to have a potty.   :smile:)  

I've also seen non-electric composting toilets advertised, but don't know much about them, other than they look interesting.

As for beer, wine, etc., someone suggested it might be good to have items like these (cigarettes too) on hand, for trading purposes.  (We don't use these items, so I'm not sure of their storage requirements.)