There will be no safe paper asset. A Paper asset relies on Law to be protected, and the people making the laws will be able to take anything they want on paper.
Hence you 401K is easy pickings-- a big pile of money, held in the hands of a 3rd party, who is easily bullied by if not in cahoots with, those making the demands.
You need things to have and to hold. If you are prepping that is food, energy production, shelter, security/firearms, toiletries, transportation, bullion and yes a pile of fiat cash. . If you have money left over, then bullion is still your best bet. Also, don't consider this an opportunity to "get rich". Being rich in the future will be living as you do now. Your goal at this point should probably be preservation.
I do not believe, gold, silver, copper, platinum, etc are in a "bubble" - they are accurately reflecting the state of the world fiat currency market. Yes, you CAN invest in the currency of other countries. China is even allowing you to keep accounts in Chinese currency if you use their branches in America.. problem is those banks are under American control ( Argentina took deposit is in American Dollars and forced the depositors to accept the local revalued currency in exchange) - but right now other currencies are just as unstable- added to the fact that trade is now so interconnected that even "secure" fiat will be shaky. If the dollar tanks, the U.S demand on the Market disappears, and that takes a lot of revenue off of the tables of foreign companies as well. Money is a symbol of value - and the less value people trade, the less the money is worth. It really is that simple. So some holdings in various foreign currencies is probably a good idea. And its probably a good idea to have those holding in cash, and in your possession . (and no a Bank deposit box is NOT in your possession)
In the end Gold, Silver and other metals will be worth "something" and be seen as a reliable symbol of value (i.e. money) - however the government might make them illegal to own - forcing you to a black market to use them. What is important to remember is that gold and Silver are just shiny rocks. Silver has industrial uses - which make up 90% of the demand. Silver WILL loose value as production slows. Gold has really no uses, and is the more reliable barometer. Both silver an gol, however, have been used as money in the past. If and when they are again recognized as "money" their value will increase on that basis. There will probably be a panic/bubble (I don't think we see it yet) where prices will go stupid.but that will be because other mediums of exchange ( fiat) have gone stupid in the other direction. This will be a good time to cash out some holding and pay down any debts you might have. After the panic buying stops, gold and silver will find a new level, and will probably buy slightly more than they cost in 1990's dollars. (around $3-5 1990 dollar purchasing value for an oz silver, about $200-300 oz gold) Of course what is available for purchase and at what price may change dramatically because how much is produced and how much is demanded will be dramatically different from 1990, and its hard to see if demand will fall the same amount as production . Housing will probably be very cheap. Fuel and Food very expensive.