Depending on who you talk to, this term can refer to either:
(A) an iron-bound wooden box full of gold and jewels that pirates bury in the sand for later retrieval
(B) the warm and delightfully-soft/smooth front upper-torso of a voluptuously-endowed female human, complete with lusciously-bountiful cone-shaped "treasures" and a comforting heartbeat.
Hey, if ya wanna talk "treasure chests", any normal dude who's worth his "family jewels" knows that a "chesty" gal's warm and ample "treasures" are far more desirable and satisfying to cradle and savor in your comfort-craving paws than a few "handfuls" of lifeless cold hard pieces of eight or silver coins.
A box where one keeps all their freaky sex toys, and accesories (such as S&M or bondage gear). Usually hid in a dark closet, attic or under one's bed.
I found Steve's treasure chest. It was full of anal beads, ribbed double sided dildos, handcuffs, 3 different whipes, ass-less chaps, a leash, and a gagball. Steve is one sick fuck.