Going to second thrift stores, depending location and store you can sometimes find functioning like new, or functioning but ugly things like crock pots and blenders which will save you a lot of effort and time spent on meals. Soups are the best, they're cheap, warm your home somewhat and they're easy to eat on bad teeth.

Dollar type stores (99 cent store if you're in CA) are good for staples like rice, pastas and beans if they're out at your grocery stores. Ethnic markets and pharmacies are other places to look for the three staples. Same for frozen vegetables, they're less than a third of the price of fresh and they're healthy and still taste reasonably. I'd also recommend getting spices in a bag vs the container, tend to be more and cheaper.

If you can get flour at your local store (I can't at mine, shortages are wild) you can try diy your own pasta without a machine, it takes time but if you have time its totally worth it at least once, its delicious, it'll be much wider than store bought but it won't take nearly as long to cook and it'll have a stronger flavor.

If you have space or are allowed access to land you can grow quite a bit from food scraps and seeds from things you get at the store that may grow in your climate. If you have access to a reasonable amount of light through a window you might be able to grow a small herb plant like dill in a pot, to have something green in your house imo is good for the mind. Fertilizer is nice but not necessary, you'll still get a yield, it just won't be say 100 tomatoes per plant, more like 25-60. If you have a lot of time to invest in gardening you can boost your yield without store bought fertilizer through your method of choice and the sweat of your limbs. Just a warning, lots of plants will cross pollinate, I had bell peppers next to jalapenos one year, that was disappointing.

On bad teeth clove oil/oil of eugenol is great at numbing pain until you can be seen by a dentist/dr. Ground cloves work too, just not as well.

To extend the life of electronics in general, and minding safety, imo its worth trying to learn how to solder, this is another thing I've had luck finding at thrift stores but you can get one on aliexpress (a year ago I got a functional one sale for about $17, idk what that equals in 2021 prices) and practice desoldering-soldering on electronics stuff people throw away. If you want to work on computers/car electrical you'll need at least an ok multimeter to go with it, sometimes you can find one at thrift stores or on sale at tool & hardware supply places. If you live in a big city you may be able to loan some (maybe even all) of this stuff from an electronics, plumbing and electric, specialist computer, or even hobbyist-style jewelry store (if you ever need electroplating stuff for gpu/mobo check there), usually there's a deposit though.

Something most can do is just keeping whatever computer dust free and in an environment with reasonable humidity (ideally not too hot) , maybe dust it out once every couple of months, more if you live in a dusty environment. There's lots of how tos on youtube, just keeping a rig clean and luck and you might be able to keep it for years.

Sort of similar with cars, if you can learn basic maintenance for it, keep up with it if possible, or at least know what the lights mean that can go a long with for preventing future problems (likely need oil if the genie light is on, break fluid if the break light is flashing, water if its hot, and so on). There's all sorts of youtubes for car fixes, just be wary that older cars may be easier to learn to fix but they tend to be rusty, so it's easy to bust a piece off anything if you're new or even just unlucky. Autozone and hobbyist shops will usually loan you all sorts of equipment out last I checked for a deposit.

I realize some areas have different laws on if you can even work on your own car at home. If you live with others and they have cars too check each other taillights+headlights+break lights+signals for function once a month, might save you a ticket, might.