This is a tall order. While your dubs will most likely be on cassette, you might want to consider DAT's or CD's. It is possible to get short run orders on CD's without spending a fortune. You will need to shop around to various studios, but more and more people have the equipment to do this. You should be able to pit a few houses against each other for your business.
Pictures are nice.
If your demo kit has some nice promo shots, that can add to the image you are creating. Add them to your resume and credits list. Make sure they are good. Also, make sure you package is slick. If you don't have graphic arts talents of your own, go to a pro and have a package made up.