A media kit is set out to strengthen the magazine as a brand. The things it may include could be information explaining the publications place in the market, indicating the target audience and typical reader as well as showing information such as how much it cost to advertise within one of the issues.
The media kit below is for my magazine Forgotten. It was created in Adobe InDesign. It includes a brief summary of what the magazine is about, what readers it targets, advertising costs and contact information.