I’ve mentioned a couple of times on here before: I downgraded my data plan during Covid, and haven’t bothered to increase it yet. Oh my plan, it goes to 100kbps once I run out of data. Once that happens I mostly just read hackernews comments. It works perfectly. Google search also works ok, google maps works with patience, and virtually nothing else will even load.
I spent a few months with extremely slow (single digit KB/s) internet. As you say HN is basically the only usable site. Even HN loaded very slowly though, so I would read it through w3m (text mode web browser) over Mosh (more efficient than SSH).
-- Worth mentioning that many sites will be difficult or unusable in a text mode browser, so I recommend Browsh which renders them (in Firefox?) and then converts the image to colorful, pixelated terminal art—it supports mouse and everything! (The word "recommend" is a bit strong here, but if your internet is bad enough and you need to get something done, it may be the only way to do it.)
I had to actually plan my media downloads ahead—I'd collect a list of podcasts / lectures to download and then fetch them all when I had access to decent wifi. Eventually I made an elaborate series of bash scripts with a php frontend to extract audio from youtube lectures and convert it to Opus, to save money on my fast but expensive mobile data.
I even set up my own internet radio station, an Opus proxy for Lofi Beats to Relax and Study... as they say, necessity is the mother of invention... or at least the mother of reading a bunch of icecast manpages... Wouldn't want to repeat the experience, but it was very educational!
Right now I'm on a metered connection (5GB/day), so I set my Steam download speed low enough to spread a 12GB download over 3 days... brings me back to the old days hahah.
Unlike the old days, though, you have to actively not download data, as opposed to not actively download data. For example, make sure synching to the cloud is off (moving a folder, especially if you’re not always connected can easily be an accidental replias of 10GB), making sure an OS update won’t be downloaded (easy on windows but not easy on MacOS except in the case of iPhone tethering), and be careful about browsing (Reddit or news sites can easily use hundreds of MB in a few minutes).
Little Snitch (Mac) can be very helpful in these situations. When I'm on the road and using my limited phone data for internet, I turn on the 'limited' profile where Little Snitch doesn't allow most internet traffic (with some exceptions).
Try browsh in mosh like others have mentioned, but also Opera Mini. Download Microemulator from https://storage.googleapis.com/google-code-archive-downloads..., and use curl or wget (not a browser) to download http://m.opera.com/mini.jad . Next run microemulator, set the device to "resizable", and open the mini.jad file (the menu item is "Load MIDlet from file" or something similar) you downloaded. Opera Mini works pretty well on bad connections, though every so often it shows an interstitial ad for an Opera site. Also, don't use it for logging in to things, it proxies all pages through its servers so it would be able to see your passwords. The Android version is bad, don't use it.