Rachel Bilson was back to work on the set of her latest project, The To Do List, in Calabasas, CA, Thursday. She arrived on location in casual athletic gear, then emerged from her trailer wearing what appeared to be a purple negligee. Rachel's had to cover up a number of skimpy pieces, like two crop tops, over the last few days. The movie also costars famous funny guys Bill Hader, Andy Samberg, Christopher Mintz-Plasse and Donald Glover, but we haven't seen any signs of the guys just yet. Christopher has his hands full with multiple projects and it's likely he'll pop up in San Diego next week for the Comic-Con panel of his new horror flick Fright Night.