It depends on what you want. If you are trying to get an artist deal, then pictures, press releases, newpaper articles, etc. are all needed to "prove" that you have both an "image" and are "creating a buzz" (damn I love hip industry talk!!!!). Also if you have a current CD that you have sold (from stage, from a web site, etc.) provide sales numbers. Naturally you also need to provide contact information, such as your management representation (you do have representation, don't you????)
If on the other hand you are trying to get published as a writer you need to send maybe 3 of you best songs (make sure your absolute best is first, you'll be lucky to get past the first half of the first cut). Obviously you need to put your contact info and copyright info on everything (CD, CD case, letterhead, etc. etc.) You don't really need pictures or a marketing bio, but a short bio of your writting experiance won't hurt. Make sure, the publisher deals with the style of music you are presenting - and don't try to show how many "styles" you can write in - stick with one style for a given publisher. Once your foot is in the door you can show what else you can do.
Now if you are sending a song to a specific artist (via a manager, attorney, hair stylist, etc) then the song needs to be specifically geared for that artist. Again include contact info on everything.
If you are looking for a publishing deal, make sure the vocals are way up front and make sure the singer is the best you can afford. Again, if you are presenting to a specific artist, make sure the singer reflects that. Publishing/writer deals aren't about production - they are all about the song. Obviously if you are looking for an artist deal then production and performance are important.