I won’t tell you what to stock up on because other than food items that are difficult to grow in large enough quantities for yourself, I’m not sure that’s the right question for someone with access to a bit of land. What I would want to do in your position is start setting up systems for reusing what you have efficiently, and cutting down on future costs, since that’s where you’ll make the biggest impact. I’ve been on the brink of unstable for a very long time, and I’ve become very good at not falling over the edge, so this advice comes from there. Nothing you can stock up on will last long enough in useable condition to make a really substantial difference long term. Except maybe cinder blocks and bricks if you are handy enough to build stuff, and canning jar lids. Maybe a nice set of rechargeable tools, a bunch of fasteners, stuff like that.
Instead of buying fertilizer, chickens or quail and various kinds of compost are great options. You can make a couple different compost containers/piles using things birds can’t eat for worms and soldier fly larva, the birds love them and they are super healthy foods. Add the dirty bird bedding to the compost once you’ve let the birds eat the larva, let sit for a bit so it’s not so “hot” and till into garden soil. The bird-poo-rich compost is just amazing for plants. Worm compost runoff liquid (because it is done in containers typically), aka worm tea, is more of a potent liquid fertilizer you can use throughout the season as needed, so they work well together, and reduce your waste. Worm castings are a super great soil addition when you till or top-dress. Then you can supply eggs and fishing worms to people for income if you want. Plus chickens can eat most garden scraps, like leaves and spent flowers, so literally free food!
Look into permaculture plants that you can plant once and harvest for years to come with no effort, and give them the absolute best planting conditions you can manage based on whatever they need. Fruit trees, shrubs, vines, and bushes are great, but if you are willing to expand your horizons and plan ahead for maintaining them, there are plants that can be eaten in a variety of ways including as salad greens, and will come back for 2-20+ years. I would suggest to focus your efforts very heavily on stuff that will continue to bear food long term because it’s no effort for all that stuff, so you can put that effort into a garden of single season crops that round out your needs rather than struggling at addressing all of them. Plus you can plant smaller things like rhubarb, mint, chives, asparagus, strawberries, etc. around the footprint of the bigger stuff and everything is happier with the reduced direct sun (“full sun” doesn’t mean all day). A big key here is variety. You want as many different permaculture plants as possible growing (tho keep in mind cross-pollination requirements for things like apples and plums that need a bloom buddy) because if the local climate shifts and something fails, you are more likely to have things that survive and are already producing, no down time while you replace what failed, and that’s huge if you are relying on it for sustenance or income. You’d probably be really surprised at the sheer variety of things you can get to grow even in the frigid north. That’s what you want to stock up on now: permaculture plants. Seeds or cuttings or grafts, whatever you need get those going.
Set up rain barrels or create a pond that you can use for watering. Maybe set up an automatic drip irrigation system from it to reduce your effort and ensure consistency. If you want you can grow aquatic foods in a small pond or rain barrel, and/or raise fish if you have enough space. If you do rain barrels and they aren’t huge, you can put guppies in them seasonally, which will reduce mosquitos and produce a lot of guppies (they typically do not eat their own young) which can be harvested to feed to chickens or fish (like perch) as well.
Consider building a well-vented greenhouse to extend your growing window and help prevent weather related growing problems with more sensitive plants. If you live somewhere with cold winters, and you can source large used barrels (and if you live rural you probably can), you can fill them with water, paint them black and place them somewhere in the greenhouse that gets sun, and use them as freeze-resistance for your plants. Sometimes this is enough, if you build it right, to keep plants growing year round even up in Canada.
If you can, build a root cellar somewhere to store whatever you manage to grow, and learn how, and how long, to store each crop. It doesn’t have to be huge, but if you lose electric, it’ll still work when a fridge won’t. This doesn’t have to be a new space if you don’t want to build something and bury it, so if you have a weird empty basement room you can convert, or a crawl space or something, that might be plenty. I use a weird big cabinet the stairs down to my basement are built around and part of, because it’s otherwise a huge empty cold waste of space that’s inconvenient to access, with the door being on the stairs. A dark place that stays consistently cool and humid, but not stagnant, will keep produce good for considerably longer than refrigeration or sitting at room temp. If you commit enough space to it, you can use it to store home-canned goods (like in jars) in the dark to prevent light-related degradation.
If you don’t have one, invest in a large pressure canner, and as many jars as you can get your grubby mitts on for cheap (or free if you know people who throw out canning jars), and learn to use it. Find approved canning recipes, and save them somewhere offline. (the USDA actually has a ton of tested and safety-approved recipes for home canning, or you might be able to find books at local thrift shops. It’s wild what you can preserve with a bit of forethought!).
If you don’t already have solar, consider looking into it. It’s an upfront cost, yes, but it will save you down the line, especially if the grid, or the value of money, goes wonky. You can buy everything used from solar farms for well cheaper than new retail prices, and have someone install them or do it yourself if you feel comfortable, but then have it inspected and hooked up by a professional. The panels and stuff coming from solar farms still have most of their effective life left, they just cycle them out on a schedule to produce peak energy. If you go this route, make sure you have a way to disconnect from the grid if it goes down so you can continue using your solar. That might be standard, I’m not really sure. If you think inflation will make your savings worth less than not paying for that ongoing bill, it might be worth it. Keep in mind that you can always add more later if you need to, so don’t think you need a $20k system upfront. You might be good with $5-10k, which buys you a LOT of used solar capacity if you have space for it.
Have to be pianos. If you use a safe they just open the door and walk out.