Utilities I use
Note: nothing here is intended as novel analysis. This is very much a "write something in public once instead of in private N times" post.
I don't install a ton of utilities on my computer, but I swear by a few of them:
Clipboard management
Right now I'm on Pastebot, but the difference between clipboard managers is small compared to the difference between using a clipboard manager and not using a clipboard manager. (MacOS now has more advanced clipboard management, and I'm keeping a close eye on it.)
Yoink
Yoink is a "shelf app:" it gives me a maximally ergonomic way to get files (and more) into and out of a holding pen. So, if I grab a screen shot and want to drag it into a window that's hidden, or that doesn't exist yet, Yoink makes that simple.
Again, there are other apps for this, and if you know all the key combinations, MacOS itself supports advanced dragging and dropping. But I'm quite happy with Yoink.
Advanced screenshot software
I'm a CleanShotX guy but have also used Snagit happily. The built-in MacOS tools have come a long way, but I still prefer to have an advanced, extremely ergonomic screen-shot tool available to me. Giving people helpful, annotated screenshots within seconds is a communication superpower.
...and that's it! Some people use many more utility apps than that, and many use none at all; those are the three I'd want on any computer I use.