My son is 7 and sounds just like yours. He never played with toys as a toddler. He would find anything in the house that was NOT a toy to play with. He also loves music, so we just did alot of things with music to keep interaction going. He also became obsessed with cars, (real cars), but he would carry around little toy play cars although he didn't really play with them, he just liked carrying them around. He also liked stuffed animals. Have you tried acting things out with stuffed animals?
Eventually, he developed an interest in drawing, and he would sit for long periods drawing on paper and then he moved on to a magnadoodle. He still draws on his magnadoodle to unwind.
I feel your frustration, but one of the blessings is that our children don't have to have a lot of toys to make them happy. As long as you are interacting with him in things that interest him, then that is what is important.
I am sort of happy that my son is 7 now and the emphasis at school is now on learning more instead of focused on playing. I know playing is very important for development, but my son just never really got into toys they way most kids do.