What token does Cinna bring Katniss as she dresses in The Hunger Games?

Cinna brings Katniss the token of a gold mockingjay pin.
It's just as well that he did, because Katniss had forgotten all about it during her training sessions. It's a long-standing tradition of the Hunger Games for those taking part to wear something that reminds them of their home districts.
In the case of Katniss, the image of a bird in flight is supposed to remind her of District 12, which she will represent in the Games. As well as being one of her father's favorite birds, the mockingjay is renowned as a free-spirited creature and is therefore an appropriate symbol for Katniss. It also serves as a symbol of freedom in general.
As he pins the mockingjay pin on Katniss's outfit, Cinna tells her that it was almost forbidden by the review board. They were worried that the pin could've been used as a weapon during the Hunger Games, and so came close to banning Katniss from wearing it.