The power antenna comes to mind. I would suspect any audio power amps not factory installed, maybe even those factory installed.
To find the problem place an inductive ammeter over the battery cable and start pulling fuses. Look in your wiring diagram for all circuits powered when the key is off and disconnect them. The alternator is one of those circuits that a fuse will not disconnect.
Bosch Master, ASE Master, L1
33 years MB technician