FWIW, I interpret the question as being strictly about stuff one built for oneself in the context of everyday, day-in, day-out life. Stuff to use yourself. And on that front, I just realized I almost never build anything strictly for myself. I work on Open Source projects and work on projects at Fogbeam that I (want|hope|expect|whatever) other people to use, or things I would use myself in a business context. But I just don't build handy little gadgets to use around the house, or in my truck, or when out and about.
This may be one of the first times I've really felt a strong case of the "imposter syndrome" that one hears so much about. I feel like I should have some answers for this, so why don't I? :-(
OK, to be fair, I did built at least one thing just for myself. I have a couple of lamps that are positioned in an out of the way location in my living room, and I hate having to walk to them and stretch to reach the switch(es). So I did the whole "IP controlled lamp" thing with a relay and an Arduino Nano 33 IoT board. The power strip the lamps are plugged into is controlled by the relay, and I can send an HTTP request to turn the relay on or off. I created a shortcut on my phone's homescreen so I can easily control it from my phone. But that's such a chintzy project I almost feel worse for admitting to it. :p