I purchased a pioneer dvd drive (OEM) and it was literally just a drive sealed in an antistatic bag with an instruction leaflet.
It obviously varies from product to product, so when buying OEM, make sure you have any extras such as cables/drivers, or be prepared to purchase/download them.
Just expect to get the bare item and nothing else, and you wont go far wrong.
edit, the WesternDigital 500gb hard drive I got was litterally just the drive in a sealed bag.