Ferrets need a high protein diet. You can purchase kibble/ferret nuggets/biscuits at your local pet store or find the really good stuff like Alpha, James Wellbeloved online. Ferret's should also have a healthy balanced diet consisting of fresh poultry. DO NOT feed ferret's fruit or vegetables because ferret's are strict MUSTELIDS i.e. they are strict carnivores. They cannot handle fruit or veg as they are not equipped or designed to handle it.
Doing so can seriously jeopardize the health & safety of your ferret by feeding fruit & veg, it can lead to pancreatic diseases.
Ferrets are not cats or dogs, so they do not need treats. However if you feel the need to give them a treat, the best "treat" you can give them is love, attention, cuddles and kisses, and ferretone/ferret tonic (basically like cod liver oil).
For more informative expert advice, head over to: [www.forum.ferret.com]