My top ten biggest users of space on my iPhone at the moment:

Music 47GB
Photos 13GB
Videos (a few TV episodes I have queued up to watch, I'm away abroad on holiday at the moment) 7GB
TomTom 2GB
Overcast (podcasts) 2GB
Messages 2GB
Google Maps (with a few offline areas) 1GB
ViewRanger (walking maps) 1GB
iMovie 1GB
Galileo (offline Open Street Map) 1GB

I currently have ~20GB free, but that is only because I've done what I really didn't want to have to do and turned on "optimise space" in iCloud Photo Library. I have 45GB of photos/videos in iCloud and I'd really rather have high quality* versions of them all on my phone

I don't use Apple Music, I tried using it to sync my music library and it was awful. Some things failed to sync completely, some things were replaced with live versions of studio songs, some things were replaced with unrelated tracks, etc. But to be honest even if it worked, I wouldn't really want to use it, I want to have all the music available without worrying about whether what I want to listen to isn't on the phone when I have a crappy Internet connection.

All the real data on the phone is backed up in multiple ways.

Hopefully I'll have an iPhone some day with 256GB of storage and I can turn "optimise space" back off in iCloud Photo Library

* I think I've said it here before, but I wish iCloud Photo Library was more clever about how it used space with "optimise space" turned on. I'd like it to use some of my 20GB of spare space to cache some larger image previews, I'd fed up with saying "let me just show you photo of X" to find that I only have the thumbnail image of the photo and I wait the next few minutes for a viewable image to be available