Additional information to a post in sidebar

Hi all,
The website I am working on calls for the ability of the author to be able to add additional information about the post in the sidebar. So what I am thinking is there be another box below the content box on the edit page (much like excerpt is) where they can paste the copy in and then it will be automatically populated in a location in the sidebar. This is so it can be customized per-post.

I don’t know if there is a widget/plugin that can help me achieve this or if someone could have me with code. I am an intermediate beginner to wordpress but have been working with HTML and CSS for about 5 years now.

Any help would be greatly appreciated.

Thanks!