Hands-free options for Android?

I'm curious what other Android users are using to do stuff "hands-free" while driving (without changing the OEM head unit if it matters). Using Google Assistant or some other app?

Currently, I just use the head unit's bluetooth ability to receive calls (and texts if phone is open). Other than using the soft buttons on the Home screen, I don't think I've tried to make a call while driving.

Ideally, I'd also like to do stuff like search GasBuddy for Shell stations along my route or control Hoopla (library audiobook app), but not sure that's even possible.

Mainly asking since my state just joined the hands-free bandwagon, plus I have a long road trip coming up where I'll be passing through others.