Something you're just good at with minimal effort and/or you learned much more quickly than average.
For me, it's paper snowflakes. My brain just seems to effortlessly figure out what cuts to make to the paper wedge to make it turn out exactly how I want it. Largely useless, but good fun and was a much-needed ego boost when I was a kid :]
I am a really quick reader compared to most people. Doesn't sound that amazing and it's certainly not unique, but it comes really handy. Always helped me with exams, as I got some precious minutes more to actually work instead of reading. I can go through books and articles really fast. Retention is not amazing, I'd say it's about the same as when most people read in their normal speed.
I really envy the people that can read quickly and retain everything. But I am also content with being relatively quick.