For emergency purposes some people are buying gold, to have on hand and preserve wealth. One problem I have with that is someday the Government may outlaw gold as a form of payment, as was done in the Great Depression. Also it does smell kinda apocalyptic to me. Storing in US paper dollars may involve the extra risk the USD has some real issues in devaluation. If that happens a little nest egg for emergency purposes may not be worth that much when needed.
Another way to have some cash on-hand and have it rise in value is US coins. Not all coins mind you, certain coins that are valued more in material (metal) than the face value. One example is the US nickel. Did you know that one 5 cent piece (US Nickel) is about 5 cents in raw metal? There are better returns on investment in older coins, but on the nickel you can go right to a bank, get a bunch, and ensure it will always have a reasonable value no matter what happens to the US Dollar valuation.
As USD strengthens, the nickel will in-fact retains it's 5 cent face value, but may be worth less than 5 cents in material. So no matter how you look at it, its a pretty safe, but not very practical, storage of purchasing power.
For more on coins value in the material visit http://www.coinflation.com/
And once again, thanks to reader Ryan Swan for the link.