shoes. though not technically expensive because i buy them used (they are expensive when bought new).
cheap shoes will hurt your feet, are easily damaged, and not repairable. the cheapest shoes i had lasted 2 weeks. leather ones can last years with proper care and resole.
bamboo socks. they have better odor resistance than cotton ones.
getting sick of my cheap earphones, on the hunt for a php500-1000 corded earphone.