If you do have some sort of employment agreement, you may find that it has a provision applying the laws of a different state than the one you are working in. These choice of law provisions typically are enforceable, so be careful in presuming you know what the law will be in the event of a dispute. You may be surprised. An employment manual can be a good way to show employment is not arbitrary. The employer should make it clear that the manual is policy only and not contractual.
Employers put lots of things in an employee manual.
Sometimes this is good and sometimes it is not. In recent years, primarily because of litigation, matters such as e-mail policy, Internet use, sexual harassment, sexual orientation and others have crept into the manuals. Many employers like to use the manual to talk about the history, mission statement and goals of the company, although this is certainly not mandatory. Get their signature acknowledging they have read and discussed the manual and policies with their supervisor and keep this document in their employee file. Have your local legal counsel draft the document for you.