Physical changes are also welcome, so things like skins, cases, screen protections etc... are fine to discuss.

For me, in this order:

• Wi-Fi calling: it was very surprising that this was not on by default, and enabling it helped a bit with the battery life on my Pixel 7a;
• Try custom launchers: I was happy with the phone but the very first annoying thing is the damn Google search bar and how there was no way to just hide it like any other widget. So I ended up installing KISS Launcher (it's FOSS and still maintained);
• Bite the bullet and install GrapheneOS: you get more security, sandboxed Play Services, a more fine-grained permissions system and you can still install the default Pixel apps from the Play Store while cutting off their internet access, and most importantly you get rid of the Google bar (also enabled Wi-Fi calling as previously done).