One of the online resources I use frequently is the Quick Guide section of the Chicago Manual of Style Online. I have a hardcopy of the manual at home, but the size of the book means it does not travel with me. It is hardly pocket sized! The Quick Guide, however, goes wherever I go that has internet. Whenever I need to check the format for Chicago-style footnotes and bibliography, I can just click and check. So whether you are an old hand at Chicago footnotes, or it is the first time you are using them, this is the online resource for you.
Best, Dr. Ferdinando