Different websites and different pages will have different needs from their footer. When considering what to include be mindful of a cluttered footer, it is essential that you include only what is necessary. Start with the conventions, this includes your contact information and social links and may include support links.
Here are some suggestions for what to put in a footer:
Don't skip on design elements for your footer, your footer can be fun, visual and always on brand. It's important to consider white space and think in terms of columns/content blocks. You should also focus on creating a visual hierarchy, this can be done by creating headers for content buckets.
Too many websites dump a bunch of links in the footer, where instead it should be clean and selective. Your footer should not be used a collective of all of your links nor should you use the footer as an attempt to drive SEO.