I don't really use Android much now that I daily drive a Linux phone, but when I do these are my go-to apps:
F-Droid: FOSS app repository/"store" where I get most of my FOSS apps.
Aurora Store: FOSS app that interfaces with Play Store, allows downloads without account or tracking
NewPipe: FOSS YouTube alternative with the ability to download videos
Fennec: Fork of Firefox in F-Droid
VLC: Media player that plays almost anything
Hacker's Keyboard: My long-standing favorite on-screen keyboard of any platform
Terminal Emulator: Before I got into Linux phone, for running Linux distro chroots