You want a mix of toss toys and hanging toys. Good toss toys include solid chin safe wood blocks and balls, willow balls, loofah slices, bamboo crunchers (finger traps), willow shapes and things like that. Hanging toys are just blocks of wood and/or other things like loofah, hay cubes, popsicle sticks, lava chews things like that strung on a wire or chain. If you look though the vendors on here (banners on top and classifieds) there are tons of toys for sale or to give you an idea of what to make. Adding bells (stainless steel) to hanging toys seems to interest a lot of chins too. Another thing, especially if he use to have a mate, is a
cuddle buddy, which is a fleece stuffy shaped like a chinchilla, assuming he doesn't eat fleece, it gives them something to sleep and cuddle with and pulls around. Some chins also enjoy tearing up paper bags, put treats or hay inside to make it interesting. Also most chins like tearing up cardboard, so the parrot cardboard bagel bites work well, same with cardboard boxes and tubes. But you do have to be careful since some chins do eat cardboard, and ingesting too much can cause an issue so it needs to be taken away if they eat it.
Basically chinchillas are about as smart as a parrot, so they need roughly the same amount of mental stimulation in the form of toys. Which also means you should rotate toys, or at least move them around in the cage from time to time to keep things interesting. Just remember that chins chew everything, so anything you put in the cage has to be safe to chew on.