I cannot emphasise the need for a towel strongly enough. From the above posts, it is conceivable that you may not have got this one on your list yet.
Luggage rack - but you may not want side screen storage so use the car a bit before you spend on this. Side screen storage in the luggage rack is very useful if you remove the side screens when touring. But, it leaves your luggage a bit higher reducing your rearward view. If you find that you leave the side screens on all the time when touring, then a lower luggage rack could be your better choice.
Paint protection film - while the paint is still new. You will not regret it.
Microfibre cleaning towels and Meguairs ultimate detailer.
Enjoy your new P&J.
