Just got mine 4 days ago.
I still need a screen protector.
But other than that.....I have a second controller built in, had a 16 GB card left from previous use with my 3DS (stacks with internal memory), and I have a laptop bag that has served me well in carrying portable devices for years. No new purchases necessary.
I guess I'll need a games case eventually, and have my fingers crossed that more controller support is added for wired connection. I have no doubt the Pro controller is comfy, but boy do I think that think lacks style. Gonna wait as long as possible for alternatives.