A friend was a party guest in "The Great Gatsby", she spent a month of nights getting paid to wear period clothes and trying to get on camera. She had a blast, which is one reason I thought about being an extra myself if the chance ever came along.
Okay, I once walked past a local beauty spot, where there was a film crew. There was a food truck there, With one sign up saying it was catering for the production, and was not open to the public... and another sign saying "NO BACKGROUND". That meant that the extras didn't get any food truck food, and it's reportedly the same on most productions. Good food for main cast and crew, maybe some granola bars for the "background" and definitely not free drinks!
I loved doing extra work. I never wanted to be an actor, so it was fun. The pay was decent. The work was pretty easy, although sometimes a little boring. Depending on what you are doing, and the scene you are in, you can meet some pretty famous people. Plus it's fun to see yourself on the screen.
Seems a cool side job to me. No production would be worth anything without them. Imagine watching any film or show you love without the extras and just the main cast - it would look like an amateur ad lib skit.
They make minimum wage for eight hours. Time and a half for hours 8-12. Double-time after that. And most of the time, they get into double-time. They sit around most of the day reading or looking at their phones or whatever. It's not the greatest pay. But it pays the bills.
Most of them are actors who think being an extra in a movie will actually get them a job. They don't realize you don't even have to be an actor to get a role as an extra.