Specific Children's Books of Unknown Title and Author

When I was in elementary school, I checked out a series think illustrated books (I think there were two) that my brother and I really loved. I don't remember the title or author. They were about a solitary kid who always wore a raincoat and stashed its pockets with paper clips among other little supplies. I think the kid discovers a money tree in the second book, and his parents don't believe him about it. I checked the books out circa 1990 so they're at least that old.