Aniston was "in an extremely good mood" as she sampled small bites, including quiches with Just Go With It costar Adam Sandler, as well as Hugh Jackman, a source tells PEOPLE.
"The full kitchen was at her disposal," says the source, who adds that the party dined in the private third floor dining area.
The actress recently told PEOPLE that she planned to celebrate the big day by going on a getaway – much like last year's Los Cabos trip – but without forgetting her exercise routine.
"Get up, have breakfast, have a workout, do something great outside. Yeah, I know, it's annoying," she laughs. "But that way you feel great."
Reporting by MARY S. PARK