They are called a snack bar. The layout as Woodford described, all at the East end of the BRN car (adjacent to the ACN). Staffing an issue; at times they shut down for parts of the trip for operational convenience. Limited range of foods, but they cater for many dietary requirements. Also drinks, but all non-alcoholic. Everything is a compromise, both with range, layout/space, and staffing. The person behind the counter is a conductor, which they may pinch for other duties at short notice (e.g., if the rostered conductor is unavailable at short notice, they use the snack bar conductor to run the train).
All the "N" sets have the facility, but they are often not opened (e.g. on Geelong and Seymour local trips). They are usually available on Bairnsdale, Albury, Swan Hill and Warrnambool, sometimes Shepparton. The V/Line site shows which trains have them available, also the menu.