For the most part extras are fed well while working on a production. Meals are provided in some circumstances, and nearly every production has a craft service table. As a general rule meals are provided for the cast and crew and for extras when a production is on location.
Lunch breaks on location are usually half an hour and the meals are catered.
The catered meals are almost always nutritious, hot, and tasty. Extras usually have the same meals as the cast and crew, but not always. As far as providing meals, they were by far the cheapest production company I worked for. The non union extras were provided cold box lunches consisting of sandwiches, fruit, chips, dessert, and a drink. While this may not seem too bad, compared to the hot meals provided cast, crew and SAG extras, it was pretty bad, especially day after day.