Everything that you use for prolonged amounts of time every day. For me it was ergonomic chair, keyboard, pillow. Expensive is a word, but I would rather think higher quality when choosing replacement for stuff I use.
Another category of things is hobby equipment, for me it's instruments. When I buy one it's to last. So when I was buying digital piano I went for one over my budget because I don't plan to get rid of it for next 5-10 years still, and it was 5years ago. Overall stuff that you don't usually think of buying frequently.
Last category I think of i go for higher quality stuff then generic ones are travel stuff. Last thing you want during your trip, short or long, distant or near, is to deal with faulty bag, broken wheel, or such.