Treats for chinchilla

Hey guys I want to give my chin some more treats when he does something good. Right now I don't have any for him, occasionally I will give him one plain cheerio and he loves them but I don't want him getting chunky. Any recommendations for snacks for them to have that won't make him gain too much weight but also something that he would like? I used to give him dried blueberries and he loved them, are they okay to keep giving or is there something better that you can recommend?

Thanks!