For accessories, I would go with the Nokia accessories. Wireless chargers/cases, camera grip, etc.. You could try some NFC/bluetooth speakers or headphones, depends on what you're looking for.
Also, if you haven't tried, Glance and double tap to wake are two cool features. Make sure your phone is updated to the latest OS version dubbed GDR2/Amber. Also, in the settings for photos you can make Nokia Camera the default camera app, so when you click the camera button, it opens Nokia camera instead of the standard camera. One of my favorite features is voice activated text replies, so if you have bluetooth in your car, the phone will tell you that you have a text read it to you and then ask you if you would like to reply. Anyway, these are just a few tips, I'm sure other can give you some other ideas as well. Just have fun and enjoy that camera!