I am buying a boot tray liner for mine, so my surf kit and wetsuit etc, doesn't get sand a salt water all over the carpet in the boot. I will also probably buy a new plastic storage tub to put the wetsuit in and contain it in when wet. I would also get official GTI Mats should they exist, which at present they do not. Other than that probably new SD Cards to store my music on, a third spare key to take in surfing and a new Aquapac Diving bag to keep the key in.
I may also buy a load of new car care stuff.
Gone are the days of stickers in the windows, I like to keep things minimal these days.