Ngl I can't even think of anything that only costs a dollar nowadays

Foam earplugs if you're headed to a noisy area. I know too many people that have damaged their hearing by not protecting it at concerts and other venues with amplified sounds.

Not sure if this is international, but sewing machine oil is cheap and it lasts years for all sorts of things that need lubrication (not for organisms)

Condom

i had a suoer cheap keyring that kept getting out of shape and poking my leg and dropping keys that i tolerated for years. finally i splurged and bought a thicker one for $1 and it totally solved the problem.

It's a buck 25 now, but you can get two Inc brand R2 pens at dollar tree. They're the only thing I've written with for nearly a decade now. They're a smooth ballpoint with a slight bleed in 0.7 making your penmanship look bold, smooth, and steady. Everything my handwriting lacks. They now make a 0.5 and is equally as clean but far better for smallest script. One pen lasts me about 6 months of regular writing.

I don't know if they still exist. But there were these machines in casinos that took dollar bills, and always seem to pay out really well. 1 of paper equals 4 of coin everytime.

Watching the sun rise every once and a while is free. You could probably get a pen and a few sheets of paper to write or draw your experiences. By volume a daily vitamin is well below $1 per day and could have significant benefits if you're not always eating healthy.

Starting this out:

P51 Military Can Openers: I have several of these. I have one on a tiny magnet attached to my kitchen door should I ever need it. Works about as well as any other can opener. Easy to slip in a drawer, keychain, car, exct.

Mason Jar plastic reusable lids: great for storage as well as meal prep. I have a lot of mason jars and these are awesome.

Dollar Tree movie candy

Arizona Iced Tea.

The only things I can even think of that are still that cheap are like... A single fruit or vegetable, salt, and ramen. I guess bananas are cool? 🤷🏻‍♂️

A tree donation.

Cheap scissors for your car. You never know when you need to open something that would be difficult to do with your hands for whatever reason.

A few things you could probably get for $1, but would be better if bought in bulk:

A permanent marker, a package of labels. Combined, you can reuse your Amazon boxes as storage boxes. Labels aren't necessary, but black text on a white background is easier to read from a distance.

Box cutter knife/utility knife. Can be used to cut holes in Amazon boxes for pets to play in. Or, simply keep them but the front door so you can open packages right away.

Hook-and-loop (Velcro) ties for wires. Can be used to tidy up the wires behind your desk, or for charging cables when traveling.

Dish soap (without degreaser)/baby shampoo. Aside from their original purposes, these can both be used to clean glass before applying a permanent tint (or just to clean glass normally) or to wash your car (degreasers can wear away at your clear coat over time.) Both can be found at the dollar store.

Colgate regular toothpaste. (If you don't have tooth sensitivity) You don't need colgate total. You should still use an electric toothbrush. You should not use the cheap off-brand toothpaste. You should also floss.

Jellyfin/Subsonic/Plex Server If you have a digital library (movies, shows, music) and an old computer/laptop/raspberry pi, you can put one of these three programs on it and host your own, personal, Netflix/Spotify for free with no ads. You only need to pay for electricity. You need to learn a bit to set it all up, but once it's done it's very set-and-forget. You'll also need to buy or find your new media online (or rip it from a disk), which can be a big change for some.

Something else that has a low barrier to entry: origami. Learn how to make a square from any sheet of paper, then learn how to make the traditional paper crane. All you need is any piece of paper and scissors (to cut it into a square). If you enjoy making the crane, there's an endless amount of models to fold. The craft has exponentially taken off in the last few decades, just do a little searching.

The last campfire on steam when its on sale.

A vpn subscription over 3 years or split the cost with a friend, it comes to about 1 something a month. Cheaper than those shitty subscription services.

The DeArrow browser extension. Made by the creator of SponsorBlock, it crowd sources replacement titles and thumbnails for YouTube videos to just about completely eliminate clickbait.

Bitwarden Premium is $10 a year. Less than $1 a month.

Bitwarden also has a free tier.

a box of Whoppers

Flossers. Contact cases for packing lotions, hair product, etc.

There's these pineapple ginger candies in the European section of the grocery store that are 1.39 a bag and saved me during my recent bout of laryngitis.

Also their tea section is much better and quite inexpensive.

4 quarters