Ferrets eat small amounts often, so food should be available at all times. Feed dry cat food or ferret food free choice. One of my favorite ferret foods is Wysong Ferret Food. The food should have at least 38% protein. Some other good choices are Science Diet, Nutra, K&D, Purina Kitten Chow (less expensive) and Friskies Kitten Chow (less expensive).
On the market also are foods now made just for ferrets They contain all the protein, fats, and vitamins ferrets need for growth and maintenance. Some of these are 8 in 1, Marshals, K-T, and Totally Ferret.
Fresh water should be available at all times. Give water only from a bottle. A dish of water makes a great swimming pool, but bacteria grows very rapidly in the water a ferret has been swimming in and they should not drink it.
Vitamins can be given in the water, infant vitamins, which can be purchased at the drug store, are great. Give 1 drop per full water bottle each day. Your ferret should have at least 1/2 hour of sunshine through the week. This is the only way it can get vitamin D.