Congrats on the new car. What color?
The harness has always been run for the under seat sub. Don't get it at the dealer, there are many third party vendors that will have accessories for less.
If you can swing it, install a clear bra to protect the paint. I've had one on for almost three years and it has made a huge difference. Do a search on that on the forum and there is some good discussion. Spoiler alert: Those with clear bra = extremely pleased; those without it = pissed at the soft paint and wishing they had installed a clear bra...
Skip the Subie winter mats and get the Weathertech digifit floorliners. If you have kids or the back is used, be sure to get the rears as well. The Subie trunk mat works very well.
Skip the OEM mudflaps; they look ok, but that's it. They don't perform and they leave marks on the paint.
If you don't have them, the OEM fog lights work well and are relatively simple to install. Dealer markup and install fees are crazy insane.
That's a start, for your consideration.