I have an
A3, used to have an
A2 which I loved but I crashed it.
Things I bought that I used:
Strobe lights - Firehouse are great but Vifly are cheap and almost as good.
Mount to use an iPad instead of my phone - and extension cable.
Small backpack to carry everything in.
Range extending Yagi antennas. YMMV but I got a nice, modest increase in range and stability.
Things I bought but almost never used:
Prop guards
Payload airdrop system
Landing gear
Spotlight mounting systems - tried several of these
Extra camera mounts
Other:
I don't recommend the aftermarket props. They barely reduce noise, mostly just shifting the tone and can be brittle.
The landing pads can be a nice accessory.
The wetsuits sold by phantomrain.org (a member here) are very cool if you ever want to fly in the pouring rain.