Duplo. He’s really getting into building stuff with it (Nan’s house, Cranky the crane from Thomas & Friends, towers).
Some of the Thomas characters – the wooden railway ones. Bertie the bus, James, Gordon, Toby, Harvey, Salty. And there’s a Cranky the Crane at K-Mart that he really liked the look of too.
Will add to this list when I can think of other stuff.