Chinchillas have quite delicate digestive systems and so have special dietary requirements. Rabbit food does not meet the nutritional needs of chinchillas and frequently makes them fat.
The primary food item for chinchillas are specially formulated pellets. Unlike other animals, chinchillas will only eat small amounts at a time and so you need not worry about over-feeding them. However, to keep the pellets clean, we suggest you provide just a little more than they need in between feedings.
Along with the pellets, chinchillas should have ready access to hay cubes. These hay cubes can sit in the cage for many days until they have been eaten.
In addition to the above two items, chinchillas should also be given a vitamin and mineral-enriched seed mix. A teaspoon each day per chinchilla is what we have learned is the proper amount. Chinchillas will eat all of this seed mix in one sitting so you can't simply fill up a dish and expect them to spread it out over several days. Also, have one dish with the seed mix per chinchilla to ensure that each of your chinchillas gets a chance to eat it.
We've started to compile a list of safe and unsafe foods in case you choose to feed your chinchilla items other than what we've mentioned above.
The last food item to provide your chinchillas is some form of treat. Treats are chinchilla-specific products from the pet store or simple things like raisins. Our chinchillas like raisins the best. Like the seed mix, it is important to limit the consumption of these treats. Make sure that each chinchilla gets a treat by hand feeding it to them.
For an idea of what treats other pet owners use, check out poll #2.
We try to feed our chinchillas the pellets and seed mix at the same time every day. The routine seems to comfort our chinchillas. In fact, they sometimes let us know that we're late with the food by barking. We give them their treat just before we go to bed as it helps with our chinchilla training efforts.
One final note about food. If you need to change food suppliers, do so slowly. An abrupt change can be harmful to your chinchilla. The best is to blend the new food in slowly with the old food so that the transition isn't too sudden. We've done this once with and it worked out well.
Along with food comes water. We use distilled water as we have learned that tap water can contain bacteria that, although harmless to humans, can harm chinchillas. Chinchillas don't drink a lot so the expense of a bottle of distilled water is negligible.