We didn't think of anything as enrichment per se. Always had a lot of age-appropriate building materials (MagnaTiles were a lasting favorite); books, music, cars, etc.

One thing that we might have done too much of (because it was fun for us) is always play with him. He didn't spend much alone time playing and we've noticed he, versus our younger child, who got more playing alone time, has some trouble self starting activities. Could just be a personality thing.