What should I feed and how much should I feed my baby garter snake?

I just got a baby garter snake yesterday. I had a garter snake one summer in a planted terrarium but he got away. I really liked him so I got a baby snake. He is in a 4 1/2 gallon kritter keeper (Im not sure how big it is but Im guessing its about 4 or 4 1/2). It has a shelter with leaves over it and water. Im just not sure what to feed him and how much to feed him.