There are many feeds on the market today for pet Chinchillas, I feed my Chinchillas a special feed called "Mazuri" made by Purina mills. I purchase my feed from Mt.holly farm supply in 25 pound bags, Just about any farm supply that carries Purina mills can special order your feed. You can purchase feed from Pet stores and other stores in smaller quantities, if you choose to go that route however you will pay a whole lot more for less feed.
Some Chinchilla owners recommend that you only feed your Chinchilla a certain amount of food daily, I personally disagree. I feed my Chinchillas as much as they desire daily, they only eat what they need. Of coarse you don't want a overweight Chinchilla either, if they don't get proper exercise and are gaining entirely to much weight then I suggest simply cutting back on your feedings.
I also feed my Chinchillas hay cubes daily, In the wild Chinchillas would eat plenty of hays and grass, so I let my Chinchillas have as much as they want daily. Hay cubes and grass are good for the digestive system. The cubes are also good for their teeth, being that they are rodents and their teeth never stop growing they need hard things to wear down their teeth. I of coarse give them blocks of wood to chew on to help with that, Chinchillas love to chew. But remember all woods are not safe for your Chinchillas, stick with specialty woods that you can purchase from pet stores specifically for Chinchillas.
Chinchillas need fresh water daily, I give my Chins water threw a water bottle hanging on the outside of the cage, being that they love to chew up stuff.
Now about treats, I personally don't give my Chins a whole lot of treats. On occasion I might give my Chins a raisin here and there, but I don't recommend giving alot of treats due to the fact it can upset the chins stomach. However there are Chin owners who give their chins a raisin a day, that is your decision to make I am not a vet so I can only speak from my knowledge own raising chins and other pets. In the wild Chinchillas do not have alot of fruit to eat so you can see why it would upset their stomach.
Remember, whatever you decide to feed your Chinchillas make sure it is a healthy choice for the pet, a healthy pet is a happy pet and they tend to stick around alot longer if you watch out for their health.
Disclaimer: I am not a Vet, I am simply offering knowledge based on my ownership of Chins as pets, The knowledge I have is also based on the research I have compiled from other Chin owners and Vets. I recommend you do your own research and check with a Vet that has knowledge on Chins.