Madamez
You can do whatever you want.
However, if I were in your position, I would NOT be taking out a 401(k) loan. As you know, if you ever get laid off or fired or had to leave your job for whatever reason, the loan is repayable in FULL within 90 days. And if you were in a position where you couldn't immediately repay the loan, it's considered an unqualified withdrawal, which means you have to pay taxes on it at your marginal tax rate, as well as the 10% additional penalty on top of the taxes. If you can't pay, it's not a bank, but Uncle Sam who comes after you.
Now, if you wanted to actually take a distribution and pay taxes on it, I guess you could do that, instead of a loan. At least you know where that leaves you.
Of course, if you have the option within your 401(k), you can consider investing a small amount in individual stocks or in precious metals. Or, you can reduce your 401(k) contributions and instead fund a self-directed IRA or Roth IRA or use the money to buy what you need to prepare. It depends on how bad you think things will be, whether you think you'll have to repay a loan at all, and in what kind of timeline.
The main problem of course, is that none of us know when the economic collapse will happen. It could be within two months It could take another 5 to 10 years. And who knows? Maybe the government won't be able to enforce collections - or, in a collapse situation, the government could instead outsource it to private collectors who make personal visits. Isn't that what a lot of politicians want to do these days? Privatize?
For prepping, I would start small with the basics of the "What Should I Do?" series, and slowly add to that. By example, I would start with a a two-to-three week supply to take care needs due to a natural disaster (hurricane, earthquake, blizzard, tornado, tsunami). For more long-term goals, I would set up a 6-month plan of what I can reasonably expect to save and purchase and prepare within 6 months to extend out supplies or preparations to a month or two, and a 1-year plan for what to do to extend out supplies and preparations to last for up to 4-6 months. Beyond that, it's about continuing to add to what you have and making longer-term goals.
There's a great article in that series called Prepping on a Shoestring:
http://www.peakprosperity.com/blog/prepping-shoestring-how-prepare-when-...
For what it's worth, I'm the sole breadwinner of a family of four. Money is tight and we live in a one-bedroom apartment.
Poet

I'm sure this has been discussed before but don't see it listed in the last 5 pages of threads.... I am seriously considering withdrawing from my 401K to buy some necessary stuff I know I'll need to be prepared. I figure it won't be worth much after the collapse, but the goods it would buy now will be invaluable. My plan only lets me take a loan of up to half my savings, to be repaid over 5-20yrs..... So being a single mom i'm wondering; chances I'll get my money out now, safely before the banks go under (and then at that point who is really gonna be bothered with enforcing me to pay back a loan to myself and will the government be bothered enforcing the tax penalty on me) VS. chances i lose my job (i'm a nurse) and the banks come after me to repay and I can't pay.
Anyone in the same position?