First of all: this song.
(If you didn’t click the link and listen to the whole song, do it. Just fucking do it already. Simple, yet profound — it’s an all-time favourite of mine.)
That is my answer, spoken through the late, great, Nina Simone.
But if we’re not in the mood to get philosophical and I were to give a typical answer — a bourgeois answer — I would say: my laptop.
It’s the most expensive thing I own, thus, it would be the most difficult to replace. It’s where I spend most of my time. It’s what facilitates all of this, and what saves me from withdrawing into a pit of depression and isolation. Also: chess videos on youtube.