@940Person already pointed out 2 things I would've suggested. Here's a few more ideas.
Do you have the delayed interior light / map lights fitting on your roof? The delay electronics sometimes go a bit iffy. The one in my 745 did.
One other thing that's caught me in the past is a glovebox door that isn't closing properly. The glovebox light intermittently stays on, and it never gets noticed until, say, you head out the the car at night to get something you've forgotten to bring inside.
Things that will draw a little current? The ECU, to keep memory. The clock. The sound system, to remember the radio station presets. Alarm, if fitted.
If there's no remote unlocker, the central locking shouldn't drain any juice at standby. Nor should the ECC control unit. But if water / moisture has gotten into places which should be dry, they can. Leaky heater cores don't do nice things to the relay / fuse box on the transmission tunnel either, especially if residual glycol is gumming things up.
If your car had a CD stacker in a previous life, it's worth checking there's no cables sitting within puddles in the RH rear butt cheek where the stackers used to be fitted.
