While ordinary flour may have no sodium at all, self-rising flour includes leavening, which has a lot of sodium in the form of baking soda and salt. Because of that, flour contributes to the surprising amounts of sodium in baked goods. Self rising flour contains 350 mg for just 1/4 cup.
According to the CDC, bread products contribute 354 mg of sodium per day to the average American diet. Other surprising sources of salt include dairy products (one cup of low-fat cottage cheese contains 918 mg); canned soups, sauces, and vegetables (one cup of canned tomato sauce has 1,284 mg); and deli meats (two slices of salami have 822 mg).