Feeder an RSS feed reader. It is amazing, reading all the news I care about without leaving Feeder. It saves me a lot of energy declining cookies. It is available on F-Droid.

OruxMaps is an awesome alternative to Google maps. It does require some configuration to get Google imagery working since they were required to remove it, but there's also a huge variety of other online sources it can use (wmts etc), plus off-line maps, overlays. You can use your own maps from qgis or other gis software, and there's multiple navigation options. Tracks, routes, way points, and so much more.

AnyList. I've tried many list apps and this one is easily the best. Not FOSS disclaimer. The free version has very minimal ads, it has a great, intuitive UI, you can create custom list types and item categories, it has built in quantity and unit of measure fields, and you can share/sync a list with others by email address. The amount of features included in the free version is uncommon in the market without getting more harassed by advertisements. I hope it doesn't change in the future; it's remained relatively unchanged for the 3 years I've been using it!

HiPER Scientific Calculator:
A good calculator with unit conversion (there is a free version with ads and a pro version).

Total Commander:
Good file-manager in connection with plugins for LAN, WebDAV and FTP

WireGuard:
Easy VPN Client

VLC media player:
Nice gestures for brightness/volume/skipping. Many supported file formats.

Perfect Viewer:
CBR/CBZ viewer with customizable gestures

Xodo:
PDF viewer