A4 Avant Sport 1.4 TFSI
Storage Pack is the number one thing I wish I'd added. I hadn't realised there were no cup holders or seat-back nets in the rear, in fact I haven't been in a car that's lacked these for well over a decade!
I can also vouch for bringing competition to your local dealer, I ended up with a better price than I got elsewhere.
Wait, what! Can I retrofit rear cup holders? Seriously, this is a thing. I have two small children.