What did Lily receive along with the other eight and what did it represent

"Lily became an Eight and received the identifying jacket that she would wear this year, this one with smaller buttons and, for the first time, pockets, indicating that she was mature enough now to keep track of her own small belongings."

This means Lilly is able to begin her volunteer hours. It is another example of indoctrination by the elders meant to shape children from a young age.