If it is simply a financial crash, and does not lead to major infrastructure loss, or war, and there is no major human die-off, then:
Savings will either be seized by the government either directly, or through emergency banking legislation, or an executive order, in order to stave off the event. Basically everyone that is not an ‘elite’ will lose all their savings that they do not manage to spend first.
401(k)s (and other types of savings/retirement plans) will most likely be seized the way cash will, or all such accounts will be frozen until the situation is resolved. Which means, if it is not resolved (and probably even if it is), that money will never reach the hands of those that it actually belongs to.
Banks will close, either due to actual failure, to protect themselves, or by government order. Except, of course, for their collections departments, which will be extremely active in collecting any and all debt owed to them. With bigger banks forcing smaller banks to do so in order to collect the money the smaller banks owe them. There may (or may not) be some limited amounts of withdrawals early on, but they will not last long, and then the banks will be locked up.
Initially, the government will mandate that whatever current US dollars are in circulation be used, at a set value in relation to various products. Use of gold and silver will be restricted and probably confiscated. When the black markets get out of hand, making US dollars effectively useless, everyone will be required to go with electronic accounting, probably with an initial amount credited to every Social Security card holder, by the government, with things going from their.
After that, if there is still no war going on, infrastructure failure, or large human die-off, some sort of new currency will be issued, and a more controlled economy will be put into place. Perhaps even a currency based (loosely) on the gold and silver confiscated, and even more likely it being an electronic only currency, with no paper/metal involved at all. Lots of tracking by the government, wage and price controls, limits on how much people can buy of many different items, etc.
Now, if the infrastructure fails, or civil or foreign war begins in earnest, or there is a large human die-off, then things will be very much different.
No matter how bad things get, a financial apocalypse or physical one, someone will be by to collect on a person’s debt. Might not be immediately, or even the person that gave the credit, but someone will want to be paid back.
And while you cannot get blood from a stone or turnip, they can get it from you and/or your family.
There are more than just one or two ways to pay back a loan or pay rent. They might not want money. And the legalities now, that can be administered in court for redress, on both sides, will not necessarily be available in the future. It could be illegal, immoral, and wrong on several levels, but that will not always stop people from doing nasty things to get what they think is owed to them.
When it comes to possession and/or occupancy, they might not get monetary compensation, but mostly likely will be able to repossess whatever it is you have, or evict you from your location, among a few other things you do not want to happen.
Again, this will be in a WROL/PAW situation, where might will often, unfortunately, make right. Depending on people to do what is right, just because, will only lead to disappointment and probably harm.
This all means that you cannot forget to plan for your financial life in the aftermath of a major event. It could be some time before your regular job, or even regular economic methods and systems will again be up and running in a practical, reliable, and trustworthy way.
It is very likely that you will need to have a way or ways to generate an income that are not based on what your current employment might be. If you are a farmer, sure. If you are a stock market broker and there is no stock market, you will need another means to earn the currency that is being accepted by those around you, to purchase things that cannot be bartered or traded for, or PMs are not accepted.
It does not matter what the currency is, you simply need to be able to provide a good, product, or service for which people will give you some of that currency or items with which you can obtain it.
So says the Devil’s Advocate