A set of cheap IKEA Brio-a-like wooden train track and trains. My nephews have amassed tons of it, along with a few special proper Brio bits for birthdays etc.
At 2, he'll need help putting track together, but will be able to link the locos and trucks with the magnets and push them round fine. It's also amazing how quickly they learn that two alike magnets don't stick, but repel.