I'm actually a little surprised that noone mentioned offshore accounts (as in the much-ballyhooed "Swiss Bank Account"). AFAIR, you can have well-protected accounts in Switzerland, the Bahamas, the Cayman Islands, and probably elsewhere.

Also, definitely keep some cash around, but don't go too crazy, as in a real disaster, cash is useless. Maybe twenty of every bill from $100 on down and a single standard roll of each common coin for each person in your group/family. Plus, twenty each of some small gold and silver coins. That's only 3-4K per person--small enough to carry, legal to transport out of the country, and enough to get you by for a bit.

An AMEX account is a good thing to have, but I've run into troubles in areas with bad network connections (Italy, for instance--VISA/MC worked much better for me there, despite multiple visits to the AMEX office in Roma). AMEX is great because it's nearly universally accepted throughout the industrialized world.

USD can always be exchanged for local currency, but it's probably not a bad idea to keep some Loonies and/or Mexi-pesos around if you live anywhere near the borders, or Euros/Sterling if you travel there frequently.