Not much. Have most notifications turned off across the watch and the interface is often too small for my old fingers.
Though, I do have a few installed for complications and notifications. The only one I actively use outside or heart rate, ecg, and workout is OurGroceries. However it is nicer to get my Forticlient VPN key on the watch over the phone. And the Stand Up app notifications are much more recognizable than Apple’s default notification. I do use ECG, Heart Rate, oxygen levels, and mindfulness on a daily basis.
Mostly I just use my phone still. Don’t think I would be able to leave it at home. Many apps like reminders, calendar, home, phone, and messages are really only useful to me on the phone.