What are some snacks or treats rats like to eat?

I got a male today and will be getting a female very soon so I was just wondering what small snacks or treats they like to chew on.

I heard they like to eat Cheerios, so I might try that. Any fruits or vegetables they can eat? Seeds?

I see some eat sunflower seeds sometimes, but I'm not sure if I should get those raw sunflower seeds from Home Depot or get the cooked salted ones from the store.