You could find locally-grown produce, items of clothing that the seller has bought in bulk, purses, used books and movies, jewelry, cell phone accessories, and more.
You should expect to find just about anything your looking for , from furniture, dishes, wall hangings, clothes, antiques, large and small appliances, things seen on TV like shammies, rug cleaners, etc....
Just about anything! Flea markets carry an eclectic array of items. You can expect to find a lot of clothes, knick-knacks, toys, music items (cd's, tapes, even records! ), videos etc. Pretty much what you'd find in a thrift store, you'll find at flea market only on a larger scale.
You should expect to most of the items in a flea market to be used or vintage. Everything will be at a lower or discounted price and lots of things will be from years, if no decades ago.