Note that having a press kit is not vital/essential to get press coverage…
Think about it: An editor is interested in your game and wants to write about it…
now he visits your website and finds all the necessary stuff (screenshots, videos, additional info) with ease.
As long as your website provides the needed material there is no real need for an official “press kit”.

However it is useful to have one because it makes the life easier for editors.
Therefore I have compiled a list for you that shows the ingredients of a “press kit”.
Consider to have an extra page on your website that offers links to all these things.

Contents Of Press Kit

Screenshots / Images

• High Resolution Screens (Show them off in a gallery so they can be downloaded individually and offer them also all in a zipped pack)
• Optional: Logos & Concepts or Artwork
• Note: Don’t add any watermarks. It’s simply annoying and also not favored by editors.

Videos

• Trailer & Gameplay Videos (YouTube)
• Optional: Offer High Resolution versions for downloading (However this is not essential because 99% will use YouTube videos anyway)

Press Coverage

• Links to Reviews & Interviews

Game Info Fact Sheet

• Game description
• Key features in bullet point form
• Release Date
• Platforms
• Price
• Contact Info (Name, Mail, Skype, Twitter, Facebook)
• Company Bio (optional)

Example of Press Kits (Games)

• Frozenbyte
• Tiny & Big
• Max & The Magic Marker
• Mommy’s Best Games
• Wolfire
• Musegames
• Nitako

Example of Press Kits (Companies)

• Dropbox
• Adobe
• Posterous
• Moo