to me a BOS is a good place to collect thoughts, write down spells, and general information, but i also have a 3 ring binder for things i find and print out from the internet. hope this helps...
There are so many lists on the internet as to what things you COULD put into your BOS; so many different topics you could cover in your book. Here are a few places that have lists such as what I am talking about. They may be of use to you :D
When I started out I had the same question as you - most likely, the majority of people coming to the path without a teacher hovering over them have wondered what to include in their BOS'. So I hope these links help - if they do not, you could always do your own search on google or another engine "What to include in a book of shadows" - there are thousands, if not MILLIONS of websites out there with useful information :D
I haven't had a chance to read all the comments. Some have mentioned a book blessing, the rede, and so forth. The Rede I would say is a must for any book of shadows. Something I plan to add to my own book eventually are some of my family traditions that have been carried out through the years. They aren't necessarily related to the craft, as I am the only Wiccan in my family. They are traditions I am carrying on with my husband and will continue to do so with my future children...such as Christmas traditions (the ritual of setting up and decorating the tree and so on). I want to leave more than just useful spells and info to my children when I pass on my book. Anyways, that's just an idea for you. Really you can add anything you want to your book.
MM, I have found these comments to be very helpful and have used them to begin my BOS. Thank you and BB.