... But Nellie's isn't the only place encouraging patrons to don a onesie this weekend. Three days later comes Sunday Oneday: A Onesie Party at Number Nine. ''We wanted to have an event with a bunch of people in Onesies, who come out drinking, listening to some music by the fireplace at Number Nine,'' says Number Nine's Aaron Riggins. Those who do so during the party's first hour, starting at 4 p.m., will be rewarded with $1 rail cocktails....