some random information stolen from mmo champion about things you can or can't get from bonus rolls, since i was always under the impression that you could get anything in the loot table from a bonus roll:
Garrosh Heirlooms and Bonus Rolls
Many players have asked about if it is possible to get a heirloom from a bonus roll, but @olandgren let us know that you won't get heirlooms from a bonus roll.
"Can't bonus roll them at all on any difficulty. Confusion results from them both using personal loot."
Quivering Blob (primordius lfr) can be won with a bonus roll, and doesn't take the place of an item you would have won.
Dark Quivering Blob (primordius normal / heroic) can not be won with a bonus roll.
Nalak, Oondasta, Galleon, and Sha of Anger mounts can be Bonus Rolled. Raid mounts cannot.
Reins of the Astral Cloud Serpent (elegon normal / heroic) aren't (and have never been) Bonus Rollable.
Kor'kron Shaman's Treasure (dark shaman, shaman only) cannot be bonus rolled.
You can bonus roll Siege pets in appropriate difficulties due to community feedback about Quivering Blob. The pet is a separate roll from items, so it doesn't have any impact on winning other loot.