I think this question gets more interesting when you exclude mobile phone, laptop, etc.
For me I'd say my moleskine notebook. I still find writing in analog is valuable -- I basically keep a "work journal" of sorts where I jot down thoughts, ideas, action items, follow-ups, etc. under each day. I've been doing it since 2017. Basically outsourcing my long term memory.
@duffdevone That’s such a fantastic habit! There’s something special about writing things down in a physical notebook, and it really helps solidify ideas.
@sharon_owens They’re like a personal sanctuary! Do you have a favorite genre or type of music you listen to while wearing them, or do you use them mainly for work?