A lot of good advice on this thread, particularly the emphasis on social connections and food. Given OP asked to assume near or total economic collapse though:

1. Some people advocated building up money savings. If you are convinced there will be runaway inflation (part of what I assume is meant by collapse) then this is exactly wrong. The thing to do would be to convert as much money as possible into durable goods while the money still has any value. Look into the history of prior examples like the collapse of the deutsche mark in 1922, and the rush on payday to buy necessities immediately.

2. Gold is also being suggested. If your threat model includes social collapse gold won’t do you much good. Gold has financial value but no use value for individuals (it is useful industrially, but not in a way you can take advantage of). Unless you’re planning to run, bulkier but more immediately useful goods like food and tools are likely to hold more value. When everyone’s starving, a baseball bat to guard it with is worth more than a lump of shiny but useless metal.

3. If you aren’t assuming social collapse, foreign currency is another option. Be careful, because you want to pick one that is not likely to track your local currency and fall together. The advantage here is that when your local currency stabilizes, the value of gold will drop quickly and it will be very hard to guess exactly the right time to cash out. Foreign currencies won’t have that same crash effect.

All that said, don’t jump into action out if panic. Take time to think it through calmly - collapse is probably not coming in the next week or two. The actions that will save you financially in a collapse can destroy you if that collapse doesn’t come. Make a plan for what to do if you’re wrong to avoid shooting yourself in the foot (or, as many people do after that kind of mistake, the head).

I’m old enough to have lived through several recessions, though I was poor for the first couple of them. I think a recession more likely than a collapse. If it’s a recession:

1. If you can keep your job you will be ok, really. Try to keep your job if you can. Yes even if they do temporary pay cuts.

2. If you’ve been unable to buy a house, a recession may make it possible. That is how we got our first house - prices tanked, we got a run down house, couldn’t improve it really but it was a place to live for a long time, and when you buy in a crash, taxes stay low here.

3. Remember there have been worse times and you are descended mostly from people who survived them.

4. Be nice to people. Always be nice on your way up, because what comes up must come down. We used to have to dumpster dive, and I have lived on the streets and in a car, don’t want to again, at all, but there are plenty of less extreme tactics - live with more people in one house, we used to have one family in each bedroom, not one person, and that makes housing cost so much easier.

#1 is really the most important though - if you can keep a job you will be ok. If that falls through, do not think you are on your own, reach out to others and work together.

Get to know your neighbors.

The network is one of the most important parts of a survival scenario.

Personally, I have met people through food not bombs that I found interesting and dedicated to a better future.

Dried beans and rice go a long way towards feeding yourself and family if food becomes a scarcity. Store in airtight containers, with an inert gas, so that what you do have does not become rancid.

A human can survive for weeks without food but only days without water. If you’re stockpiling.

Become proficient with firearms. This involves practice, and ownership.

It is almost always better to hunker down than to bug out.

Spend absolutely no money that you don’t need to. This saves money for you and keeps it out of people’s hands that don’t need it. The faster the collapse, the more equal it will be.

I don’t want to advise this, but I’m pulling all my money from the larger of my 401(k). (Keeping the smaller just in case it turns out I’m crazy, and if I am, I can always reinvest, with only some minor losses in time)

I bought a couple ATVs with trailers, with camo netting, working on filling those trailers with supplies and a lot of gas. I also bought an old jeep CJ7, with a trailer for the ATVs. Think lighters, camp stoves, portable solar panels, blankets, water filters, a good axe or hatchet, a couple knives, some emergency rations.

This is America. There’s more guns than people. Make sure you have at least one.

The economic hardships, you won’t be able to escape. When we lose hegemony/petrol dollar, it’s likely to be the fastest collapse in history.

This is just a quick summary. Some of us have been planning for something like this for a decade or more. There’s no way to be able to give you anything much more specific without knowing where you live or your current circumstances, experiences, or skills. But rely on any skills, training or knowledge you do have. Emphasize them and try to improve them. Make yourself a useful member of a rebuilt (small) society. I.e. growing, sewing, defense, engineering etc.

Whatever you do, do not give up. And be creative. Lighting a fire, and putting some seriously hot peppers in the fire can be a good area denial defense, light the fire and travel in the direction the wind is coming from.

Local libraries are a great way to substitute your entertainment budget for something more affordable. What’s more, if you volunteer and help out you’ll make a whole lot of connections who can help you back.

Save money and get to know your neighbors.

Trump probably won’t cause total collapse, so a basement full of beans is unlikely to be useful, but anyone relying on welfare or part of a minority group will need support. Savings will help with that, and could come in handy if you yourself get fired, either because of discrimination or economic recession.

or that mainstream (S&P, Nasdaq) financial investments were no longer sound, what can one do to prepare for “the worst”?

Investors that factor in world markets would probably do okay as long as you’re talking just U.S. economic troubles. e.g. right now VT (total world stock ETF) is weighted 64.70% U.S. market due to market strength. So in theory if the U.S. tanked and other countries have better markets for investing then the weights would shift to the other side and maybe being closer to 30% U.S. vs rest of the world’s markets weighted towards 70%.

Learn about gardening and join a shooting range I guess.

Do any vehicle maintenance you can now. Look up common issues for your vehicle and maybe buy those parts as they might be extra expensive due to tarrifs. If you need to you can sell them later.

Secondary used markets are going to be huge, so set aside anything you think people will want in the future. Buy an ebike just in case driving becomes too expensive. Download as much media as you think youll want because theyre trying to ban piracy sites and free options may dissapear.

Build a garden if you can, join community efforts like mutual aid, and form or join a union. We are strongest together.

As a teen we went through the collapse in the 80s when (in Canada) mortgage rates hit 21%. So Get your mortgage rate locked in now and don’t have a renewel pending in the next 2 years.

For my family in the 80s it meant most income was going to the mortgage and we had to be very frugal. We ate a lot of potatoes and beans, no restaurants ever, and no extras. My dad also hunted, left over meats went into soups.

We are currently living frugally for reasons. We buy bulk dried chick peas, kidney beans, lentils (various kinds), frozen peas, rice. We stock up on potatoes , carrots, onions and canned tomatoes. With a large selection of spices and occasionally other ingredient we can make a wide variety of dishes. Weekly grocery shop is around $35-50.

I expect for those in the USA the luxury of lavish meals will need to become more like my frugal diet.

Drop extra services…do you really need more than one streaming service, could you go without and scour the thrift store for BlueRay / DVDs , the libraries have free rentals of new releases.

Carpool. Barter between neighbours to exchange services.

Quit being poor, works 100% of the time.

Friend, you need to be a pepper!! I feel so good having extra of everything I need!

Emigrate? …or maybe stand for office.

As another has said, strengthen your local ties. In the event of a collapse, we’re all going to be affected in one way or another. I think the biggest thing is fostering a culture of cooperation rather the competition. That means avoid prepping, avoid emptying store shelves, avoid hoarding goods en masse in your basement or shelter.

I think a good first step would be to look for local mutual aid groups. Just Google your town or state + “mutual aid”. These groups are already out there directly servicing those most in need, and are the most ready to spring into action when a disaster strikes (here is some testimony about mutual aid group action during Hurricane Helene)

Oftentimes these groups are open to volunteers or donations and will be active during natural catastrophes, and I’d imagine economic ones as well.