If you are really worried about this, then I'd suggest a couple of things (in order of importance IMO):
1. Food. If nothing else, if you have a long term supply (6-12 months) of non-perishables, you'll be be able to ride out a lot of the harder times. And it provides a huge stress reduction if you are faced with a potential layoff simply knowing you can provide for your family.
2. Cash (outside of the bank). If there is some sort of crisis, then the banks may end up limiting what you are able to take out on a daily or weekly basis. If you're looking at buying stocks and things, then having a bank cash account is probably going to be enough but having a few thousand stacked away is not necessarily the worst idea in the world.
3. Pay down debt. If interest rates go up and you have a lot of outstanding debt, then you're going to be behind the 8 ball. Credit is about the cheapest it's been for a long time and if you're at the limit now, even a small increase in rates can tip you over the edge. If you're worried that much about a crash, maybe sell some assets to pay off other debt. And yes, your home value might decrease, but if (for example) it drops 20% but you have 50% equity, then the bank will be unlikely to force a sale on you at the worst possible time.
4. Liquid assets (cash inside the bank). Probably something you need to have if you want to take advantage of a drop in the stock market. Because it's in the system, you probably should still be able to use it to buy shares even in the case of the Greek style banking restrictions that were placed on them. After all, you're not taking it out, just moving it around.
5. Physical silver and fractional gold (and the like) do allow for effectively holding assets in USD, but they will probably be next to useless in a case of a total GFC style breakdown. After all, if people can't afford rent or food, they won't likely be able to purchase gold or silver. I think in a severe style crisis that they'll be the least of your worries. But - if it were to continue into a full on depression that lasted years, then it could end up being used as a form of currency that's better than AUD. So it's worth having some of your assets in cold hard commodities.
Just my 2c anyway.
