Here is something that can be of great benefit to your readers. It can be very beneficial to include, with your book, a CD that has an electronic copy of your book file. If you can, include both a PDF copy of the book plus the original file format (for information about PDF, see my post from Nov. 2009). These files will be searchable by your readers and can be a great aid to them in finding specific info that they are looking to find. You can even include, in a separate file, all the sources that you used to research and create the book. You might make another supplemental document that includes most or all of the parts of your book that were edited out. Then, if there is enough room on the CD, include JPEG copies of the pictures that you have in your book. You may have had other pictures or documents that were left out that you could include on a CD with very little extra cost or effort.
Making a CD to include with the book can even help you in editing your book. If you don’t really want to include all of the pictures you have of Uncle John in the printed book but you want the rest of the family to have all of them, then including them on the CD is the perfect answer. By putting this kind of CD in the back of your book, you will add great value for your readers for very little additional cost.