Regarding RFID. I am pretty sure that this is related to the binding device to the Amazon account. When I bought fire tv stick and turned it on, it showed already my amazon account and asked me to confirm. This could be only possible, if they read device ID in warehouse during processing my order and bind it to my account. Easiest way to do this just to read RFID tag during packaging, so they do not need to scan any paper labels on box.
For accessories: they could be used to bind them all together on factory with some special tool by scanning RFIDs fully automatically. Or may be available for QA if all components present in a package during packaging on factory, or even just for future use.