It's no secret----going to the library to check out books! I've saved so much money last year because I've set up a weekly routine of checking out and returning books, audio books, and movies. I'm a voracious reader so this really helps! Of course, I still buy some---used ones!
Second tip: I teach, so I can eat school lunches. But I take my lunch. It's more nutritious, and it saves $4 or more daily!