Tesla has been providing the front mud flaps and PPF for the rear doors for Model Y deliveries in some of the northern and western states. I have not seen definitive list of which states get the mud flaps and PPF.I don't know if it's an MYP thing or not, but my MYP came with mudflaps and rear quarter PPF installed. I had purchased a set of mudflaps before taking delivery, so those became backups (I clicked on "start return" from Tesla order history page, but nothing happened. I decided to just keep them).
I bought a pile of stuff before taking delivery. A couple of things I haven't seen on this thread are under seat storage drawer, glovebox divider, and center console storage bin sliding tray.