Dark green leafy veg are all high in iron and if you want to make doubly-sure he's getting lots of iron, give him something citrusy alongside (drink of OJ or a piece of orange to eat). If he likes mashed potato, then cheesy mash with spinach and cheese can be a good bet. Chard lasagne is also a good one.
For grown-ups, I hear red wine and dark chocolate are both full of iron. And I want to believe!