Which part of your equipment seems to never want to drop?
Consider it as of MoP loot tables only. We've got time enough to know what items is it that we always miss.
I'm usually unlucky with trinkets, I haven't got any real BiS trinket so far since DK card...
What about you?
(I'm only adding to the pool those items which can't be easily replaced, so trinkets/weapons/neck/rings, being the two last not that hard IMO.