According to Brainiac S01E03, cereal is magnetic. According to Wikipedia, iron is added to breakfast cereal as a dietary supplement in the form of elemental iron powder. I couldn’t resist trying it out for myself, and it’s true (see video below)!
Further, this iron can be extracted by grinding the cereal, adding the resultant powder to water to dissolve small saccharides etc that might be trapping the iron in the cereal, and then using a magnet to pick up particles of iron. Supposedly this iron reacts with HCl in the stomach to form soluble iron salts that can be absorbed into the body.