64gb Micro SD card. Amazon has a Sandisk Ultra for $40. Definitely recommend it.
Zagg HD screen protector. I put these on every phone I have had since the HD came out. The regular Zagg looks and feels weird, but the HD is wonderful. One problem though, when I had my HTC one, I got the ZAGG HD and had a Otterbox defender. The defenders built in screen protector stuck to the zagg and made the screen look funky. I didn't like it, so I swapped my defender for the commuter, which looked better and fit better in my pocket.
A USB OTG adapter. Wonderful little thing that can be found on eBay for like $2. You can hook usb flash drives up to your phone, external hard drives, xbox 360 controllers for games, etc. Awesome.
Oh! If you want awesome battery life, get the Zero Lemon extended battery.
I'm sure there's more, and I'll update if I can remember anything