The phrase "extras menu" refers to a section in a movie or video game where you can find bonus features or additional content, such as behind-the-scenes footage, deleted scenes, or special game modes. Full definition
A food server, for example, has sales experience (selling restaurant customers on extra menu items). (dummies.com)
The DVD's Extras menu includes ads for Strawberry Shortcake: Sky's the Limit, «Family Favorites» (a generic reel promoting numerous Fox family films), Space Chimps 2, and Flicka 2. (dvdizzy.com)
The interface is extremely similar on the user end — just missing a bunch of hard keys which need extra Menu options, plus an onscreen keyboard (extension of the SYM thing). (dealsagar.com)