One thing I started doing recently when I redeploy pop (usually due to distro hopping) is removing LibreOffice and installing the Flatpak version since its more up to date. Actually just ended up creating a bash script to deploy everything for me when I reimage.
It will mostly depend on the things that you want to use your system for. You can find a lot of great applications on Flathub. Pop!_OS includes a Flatpak sideloading application so you can seamlessly install flatpaks from the Flatpak website.
Tauon is currently my favorite music player for offline music. Unlike virtually every other music player, it takes directory structure into consideration when it imports music from your local Music directory, so it doesn't require perfectly-tagged music to be usable. It also has great support for Spotify and Chromecast.
mpv is the most efficient video player with the widest codec support
gThumb is my favorite image viewer with some common but essential editing features.
SimpleScan is necessary for interacting with scanners
Solaar is useful for managing Logitech receivers and input devices
Blueman is useful for managing bluetooth receivers and devices
Monophony is a YouTube music player which separates the audio stream from the video stream
Tubefeeder is a YouTube client that you store your subscriptions in to get a feed of videos only from your subscriptions that you can download or play in MPV
Scribus is the best desktop publishing application if you're into printing
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