All trading cards. He fronted the money to get a guy started and the business has been up and running for several years. Making money.
I am an avid baseball card collector for several decades and he learned from me the basics. He does some baseball card trading, but he specializes in trading trendy cards.
Very enterprising of your son. Wish we had the money our kid spent on Magic cards—then gave the collection to a friend when he left for college. Some of them would be worth $$$ today. The same about my "underground comics" from R.Crumb and other illustrators from the late 60s - early 70s. I put them in a yard sale.
(face palm!)