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.