I think contents are a very individual think. I went through every room in my house and did an estimate on all my contents based on them being totally destroyed and having to be replaced. It worked out a lot more than the recommended 30%.
Think of having to replace all your units in the house, kitchen, bedroom, all the contents within them. TV's DVD's, stereo systems, pc's laptops. CD's, all your clothes, beds bed linen, curtains, furniture etc. Depending on the standard of items it could work out to be a lot.