My LP's. Then my Revox A77 Mk3, bought new in '73 (from Walter Davies, then the owner/operator of a 1-man hi-fi shop in Livermore, California, more lately the developer of the Last Factory line of LP/tape/CD care products).
What, in your system, have you owned the longest?
For me, it's my Zerostat. Bought it in the '80s- most likely 1986 or 1987.