Boxed breakfast cereals vary considerably in their amount of iron. If the cereal is a whole grain, it probably has a fair amount of iron from the grain. However, most cereal manufacturers will enrich their cereal with iron so that they can make “high iron” claims on their marketing materials. The added iron is actually small iron bits, small enough that your body will be able to metabolize it.
However, there is an additional element to think about with boxed cereals. An issue is that many of us eat the boxed cereals with milk. Milk is a high calcium food — high levels of calcium in your meal will reduce your ability to absorb iron from that same meal. You will still get a bit of iron out of your prepared cereal, but not nearly as much as you might wish. To learn more, check out a peer reviewed article about iron and calcium here.
Better alternatives for breakfast include grain-based meals that do not need calcium for flavor. Oatmeal can be made with very little additional calcium and you can add fruit to the meal so that you absorb even more iron. If meat is on your diet, a portion of meat with eggs is a terrific breakfast as well.