Fractional calculator: TMC (Tape Measure Calculator). Invaluable for working out tape measure fraction math. Yes, I use metric when it makes sense. Not all materials are metric and this app makes division trivial.
Banking app. Fucking magic.
Airplane boarding passes. I only use a couple airlines, have both apps installed.
Personal news. I have recently discovered TTRSS which is a tiny RSS feed that you can selfhost and then the client on your phone shows you news from your computer
Bitwarden. All the passwords, all the time.
OpenStreetMap. Almost enough to replace google maps. I also use HereWeGo (TomTom corporation) when I need traffic data.
Transit apps for your (or any other) town. Can be pretty invasive, I recommend siloing them in the "work profile" all Android phones now include.
UnCiv. Wonderful time waster
Oh yeah, audio. I've been listening to news and narrative history podcasts for years. I finally put the Pimsleur files for learning Spanish on the phone, I don't remember which app I'm using to play them back, maybe Rocket? It's helping I think.