Congrats on your purchase!
I watched a ton of vids and tried the simulator for 3 minutes, then decided to bring it to an empty football field and practice there.
Extras I got:
DJI Strap
2 extra batts
DJI Hardshell Backpack (this is great, trust me)
A tablet (I got a used Nexus 7) (Was using my phone, a Nexus 6P and a little too small for my liking)
Sunshade for my tablet
32GB Memory card, a good fast one also Lexar 1000X (64GB not a bad idea, although I haven't filled it up yet)
As I get more cash I'll get more stuff...
Follow the laws you may have in your country, enjoy and make sure to READ and WATCH the vids.
Thanks for the info. So straight to P3. No practice first?