I fairly often go out with just my Garmin watch and an ereader (Boox 6”, which is just about pocketable).

I can sync music to it and use it for contactless payments, which is just about enough.

It’s possible to do a bit more but it’s more basic than an Apple Watch as a smartphone alternative (but much better for everything I want it for), and as I mostly use it for sports tracking and being phoneless, I haven’t set any other apps up.