The expert preppers I know emphasize that prepping for potential disaster is usually treated as an individual-level or family-level activity, but often the best strategies involve more community-level networking, such as getting to know your neighbors, understanding local 'affordances' (water, food, shelter, weapons, experts), and thinking about who your best local allies and clan-mates will be if things get rough.
We evolved to survive in small clans nested within larger tribes, rather than as individual super-preppers. So, my advice would be, figure out who the most useful 6-10 people would be who live near you, and start establishing some communication, trust, and contingency plans with them.
Epistemic status: Meh. I'm not an expert on this, just a LessWronger who spent some amount of hours looking into this some amount of months ago.
Relocating is one thing you could do. I spent some time thinking about this in When should you relocate to mitigate the risk of dying in a nuclear war? and came to the rough conclusion that if you value life at the typical $10M, it'd make sense to relocate if you assign >10% chance of being attacked.
As for how to judge the probability of an attack, you can keep an eye on the ISW's updates and what forecasters have to say, but I feel like that stuff probably isn't actually worthwhile. Instead, keeping an eye on LessWrong is probably enough.
I also explored some other ideas in RFC WWIII. I identified building a 1) bomb shelter and 2) buying useful items as other things you could do to prep. Neither seems to move the needle much though. But certain things are cheap, and so my feeling is that you may as well just buy them. Since they're cheap and they have some amount of value, it's not worth spending too much time thinking about it. Things I personally bought:
In googling around there were some other things I came across that you could buy, I just judged that they weren't worth it. It's also probably worth figuring out where you would evacuate to if you were alerted of an attack.
Having an emergency kit and supplies is valuable in enough situations to be worth it for most people, even if war is very unlikely to affect you. Do that now.
Evacuation or migration is a lot more limited. If change fees are zero, it may be worth maintaining a ticket outbound that you roll over every week, or at least figuring out where you’d go and having a plan for how to execute and what would trigger it.
I hang out in disaster preparedness spaces elsewhere on the internet, and I've noticed that prepping for a single threat tends to correlate strongly with pursuing preparedness choices that don't make sense holistically, or that decrease one's quality of life when the disaster doesn't happen.
Instead, step back and look at all the things that might kill you. Heart disease, automotive accidents, house fires, natural disasters. Old age, polypharmacy, falls. Job risks. Look at all the things that might substantially drop your quality of life: Illness or injury, financial insolvency, social catastrophes such as ostracism or targeted harassment. Form a big picture of the impact each event would have if it happened, the likelihood of it happening to you, and how much control you have over the way the impact of the event plays out in your life.
Start preparing for disasters from most-likely to least-likely. The most-likely disasters are the easiest to reason about, because they are the most likely, and thus you've probably seen them happen to friends and family, even if they haven't happened to you personally yet. Prepare for job loss, illness, injury, power outage, sudden problems with your home like fire or plumbing emergencies.
Once you're feeling well prepared for things that actually do happen all the time, test your preps. Simulate a minor emergency, such as faking a power outage by shutting off the main breaker to your home for a weekend. See how it goes, and update your plans accordingly.
Then you can start considering less-likely events, such as nuclear disasters. You will probably find that by preparing for the specific things that actually happen to people every day, you've gotten into really good shape for riding out more major events, or combinations of events (combination injury + job loss, combination illness + fire, etc).
General preparedness also tends to be flexible. If you prioritize saving up the financial cushion to keep paying rent for 6 months if you lose your job, for instance, you could also spend that on a plane ticket to visit family in another part of the world if your local area seemed about to become uninhabitable.
The one thing I think everyone should do ASAP for nuclear preparedness is to own some potassium iodide. iosat is the standard recommendation in the US, and a single-adult regimen of it is a 14-dose pack in which each dose is 130mg of KI. Considering that you can get it over the counter and it's under $5 per adult if you buy it off-brand, I find it hard to justify choosing not to keep some around, just like it's hard to justify not having a fire extinguisher even if you hope you never use it. Do not supplement KI at radiation-protective doses without medical direction, such as instructions from a public health authority after a nuclear event... But if there is a nuclear event and people are being advised to take KI, the stuff may become almost impossible to get ahold of. Think 2020 and the toilet paper.
I wonder what the feasibility is for a group of LW-ers somehow putting on retainer a charter flight to NZ?
...or it might escalate with a Russian nuclear strike against Ukraine followed by NATO counterattacks against Russia...
That is possible. But I think it is important not to treat this as one scenario in your list of possible escalations but as two:
I believe that P(scenario 1) >> P(scenario 2). NATO knows about the nuclear capabilities of Russia. Therefore attacks of NATO on Russia seem to me extremely unlikely, given the history of the Cold War.
Unless, of course, NATO (or the US unilaterally) extends its deterrence on the Ukraine (e.g., by taking Ukraine into NATO; however there won't be the necessary unanimity within NATO for that). Because attacking Russia as a result of a Russian nuclear strike on a third country (Ukraine) without explicitly threating to do so in advance would be approaching the level of craziness of the movie "Dr. Strangelove" (Russia's secret doomsday machine).
For that reason I don't spend much time thinking about preparation for a nuclear war (I am living in Germany). But what I do think to be important is to prepare for acts of state terrorism, e.g.:
a) This time it was an attack on the Russian pipelines (whoever may be responsible for that). The next time there could be attacks on Western gas pipelines or LNG-terminals.
b) Hacker attacks could bring down crucial elements of Western societies (e.g., electricity grid, banking system).
I think given this increased risk it makes sense to prepare for situations where the normal systems in a country are not working for a couple of weeks (having enough food, water, banknotes, etc.).
I treated it as one scenario mainly because I had seen on my twitter timeline that NATO had informed Russia that if they used nukes then NATO would strike back with conventional military.
I guess the Russian invasion of Ukraine can go in many ways. It might just fizzle out, or continue to be a fairly conventional war with extent limited to Ukraine, or it might escalate with a Russian nuclear strike against Ukraine followed by NATO counterattacks against Russia, and it doesn't seem implausible to me that it could spin totally out of control into a WW3 scenario. Or various other paths.
The more extreme end of the range with these scenarios seem worth preparing for, but I'm not completely sure what preparations would be the most relevant. I thought LessWrong might have some good ideas.
If relevant, I live in Denmark, a NATO country close to the core of the EU, not quite at the border of Russia but also not quite buffered away from Russia (especially if counting Kaliningrad). Though preparation ideas that are more relevant to people in other countries than Denmark are welcome too as they might be useful to someone else.