If you're close to the child, you could write a personalized book about him. It could include favorite things to do, things to eat, colors, sports, etc. Or if you have done an activity you could write about that. Maybe you have some pictures of the two of you spending time together? Then write about that and include the pictures on the appropriate pages.
What about a gift certificate to do something at a later date. Explain to him that you know he's busy now, but at a later date you could play at a special park and have a picnic lunch, or feed the ducks at a pond, or go the library and pick out books after getting a library card, or watch an elementary game of soccer, basketball, or bake cookies with you and send him home with a plate full.
Is he in school? Call the school and find out what they're colors are buy a couple of folders in those colors, print out coloring sheets from the internet.