Hilary Duff: World AIDS Day Book Signing!

Hilary Duff strolls back to her car after having lunch on Tuesday (November 30) in Studio City, Calif.

The 23-year-old actress shared her meal with an older mystery male, who she kissed goodbye on her way out.

Hilary will be signing copies of her book Elixir TOMORROW (December 1) in support of Lifebeat: Music Fights HIV at the Borders in Glendale, Calif.

FYI: December 1st is World AIDS Day, on which stars such as Alicia Keys, Justin Timberlake, and Lady Gaga will “digitally die” to raise money for the charity Keep a Child Alive.