Time. Spend time with him. Even if it's just making cookies. Let him lick the spoon, crack the eggs into the bowl, pick out the shells....
Or go fishing.
Or take a hike. Obviously an easy one, but one with cool things like a waterfall as the destination, or lots of rocks to climb over. Let him get dirty.
Spend a day making crafts. Gather your supplies for easy projects. Make homemade play-dough, homemade bubbles, goop, make a volcano with baking soda and vinegar.
Spend time reading all those books aloud.
Sprawl on the floor and color with crayons with him.
I guarantee, those days spent doing things with him will be the days he will love. I remember once, years ago, when I was oh, about 14. We had family visiting, and my 4-year old niece was too young to play with the many cousins. I frankly pitied her, so I played some stupid kid game with her for about half an hour. She WORSHIPED me from then on!
Although looking back, as a teenager, having a 4-year old tagging after you whenever you see her isn't as cool as it sounds. Maybe I should not have felt so sorry for her?

