Important navigation points can be included on the footer to help someone get to a new page when they reach the end of your content, especially on long pages.
Put a form to sign up for your newsletter, contact you or some other call to action in attempt to get the user to reach out to you.
This information, in most cases, should be the most obvious information on the website. In addition to putting this in the header, be sure this also appears in the footer of your website.
Add something dynamic like latest new to the bottom of the site in the footer to have something dynamic that the user can choose to click on.
This is a great place to have links out to all of the social media pages that you have. These can exist in the header as well.
An option for the footer is to fix it at the bottom of the page, which will mean it will be present no matter where you are on the page. This can be great for dynamic content, coupons or deals, a contact form or other contact information. It is also a great way to do something unique with your design.