The most important "extra" you can have is free - take the advice of those in the know here. Before you even unbox it, let alone switch it on, connect it to the GO app and try and fly..... before you do
ANYTHING... watch the unboxing DJI Tutorial video here (
Phantom 3 Professional - Specs, FAQ, Tutorials, Downloads and DJI GO - DJI) then read the manual.... then watch the rest of the Tutorials, then read the manuals and then watch the tutorials again, then read the manuals again (you see a pattern here, right?!).
When you feel confident enough to go try it in the air.... please don't! Make sure you use the GO simulator first.... and read the manual again!
This isn't to frighten or worry you - it's to prep you properly so you, unlike many others, don't have a crash and wreck your very expensive UAV early in your piloting experience. I didn't even take it out of the box for three weeks after I bought it! I read and listened to those who knew better and I've not had an issue (so far!) that I've been unable to correct and I really do believe this was because I took it slowly, carefully and didn't try anything stupid. Just my view....