Smartphone - Pixel with GrapheneOS or wait for a Moto with GrapheneOS.
Laptop - Used Thinkpad and install Linux.
Cars - Buy old and used or remove the cell antenna.
Fitness Trackers - GadgetBridge can be flashed onto some trackers. There could be other OSs.
Speakers - wired, I have a small pair for my laptop. There has got to be larger ones with good sound.
Printers / TVs / 3D Printers - do these not work without a network connection? Not saying they do but maybe an option.