I would always start small, and start by thinking.
What are the main things that might realistically happen in your home/area?
Power outage?
Fire?
Flood?
Maybe bad snow or higher temps than normal?
Or a job loss and lack of money?
Then think about your family situation and what you would need to manage in each scenario (do them one at a time initially - but there will be overlaps).
Do you have small DCs or elderly people to manage?
Are there people with medical issues or disabilities in your household?
What do you already have at home that is useful for this scenario?
Are there things you need to get - and are there options that cover more than 1 need or scenario or use?
So for a power outage, you need to think about heating the house (or part of it), having light so people don't fall down, having food and drinks, and possibly a first aid kit.
(You should always have a 1st aid/meds kit in the house with bandaids, cleaning wipes and some gloves, antibacterial cream, pain relief, basic meds for colds, diarrhoea, upset tum etc. You can upgrade that over time as money and your 1st aid skills allow. I tend to keep a small one in my car as well- in a plain ziploc sandwich bag, nothing fancy).
If you are involved in outdoor pursuits at all, do you already have a torch, a sleeping bag, a camping stove, a flask, a cool bag/box?
Do you have cosy blankets for movie nights?
Do you like smelly candles?
Do you have a wood burning stove?
Do you have a bbq in the garden?
What do you already have that you can use for this purpose?
If I am thinking about a power cut, I am thinking about who needs to go where around the house when it's dark. And how to keep people in just 1 or 2 rooms most of the time - to keep heat in and make it easier to light areas and manage potential problems. I clear pathways while it's bright - so there are no loose shoes on or at the bottom of the stairs, there's nothing to trip over going between the main space and the bathroom or bedrooms.
But I also think about how to entertain my people to stay in 1 place together - so might bring the fluffy throw from 1 bed, the favourite book and a colouring book from another room etc. And always find a deck of cards for endless entertainments and a board game the family might play.
Then, in colder weather, I close off all the other rooms (just close curtains once dark, and keep doors closed) to keep heat from moving from where we are, and keep cold rooms cold. In warmer weather, I am closing curtains in daytime to keep heat out and opening windows to let any breeze through, especially on the dark (not sunny) side of the house).
What food do I have that my family will eat, that is easy to prepare on 1 ring or just with hot water? What can be eaten cold? Is there someone else with power, or a gas cooker, or a local restaurant that's open, that I can ask to cook my food or I can buy a hot meal from?
To keep fridge and freezer cold for longer, I tend to take out the things that get used a lot (milk, butter, jam, juice, cheese, cooked meat etc) and put those in a cooler or even a cool bag from the supermarket. So that is what gets opened a lot - and I set a rule that DCs don't open the fridge, only DPs. What they need is in the cooler. If you have something in the freezer that's easy to reheat, you can put that in the cooler to thaw out but also keep the cooler cold for longer.
What battery operated or solar powered lights do I have? Are there solar garden lights I can use indoors and put out to charge in daytimes? Do I have spare batteries for any torches? Do I have those battery powered motion activated lights for middle of the night bathroom visits (perfect - leave them there) or to see coats in the cloakroom (take it out the use in the hall for a few days)?
Do I have, and can use safely, any candles? Only use those in rooms with no draughts, that you will be in constantly, and well out of reach of DCs in safe holders.
I tend to try and get DCs out running around in daylight and get as much "stuff" done in daylight so we have as little as possible needing moving around after dark - it's easier to cook in daylight that flickering light, and I might leave washing up until morning so I don't stab myself by accident, etc. After dark, we try to sit and play games, chat, maybe read if we have enough light etc - but also plan to get to bed early to snuggle up under duvets to keep warm.
And then I think through each scenario like that, what do I think might happen, what might I need to do for my family, what do I already have I can use in that situation, and do I need to add anything in?
So if a fire happens, that probably means leaving the house in a hurry - do I know where my important documents are to grab and could I have a set of clothes/meds for each person in a bag - a plastic bag of things and knowing I can empty a school bag to use as a backpack to have hands free to hold hands or deal with other things - could be something I would work through.
If the water goes out, do I have a water in the garden (a rain butt?) to use with a bucket or watering can for toilets, and a large pot I can fill for drinking water before the mains gets cut off? Or should I have a couple of bottles of water, and maybe a couple of cartons of juice, in the cupboard to get me started?
Do a lot of thinking before you even think about spending. And a lot of your spending can be normal things in normal shops or even Aldi/Lidl middle aisles are great for camping bits and tools that are decent quality and handy.