In my interview with Sharon Crawford, freelance writer, editor and writing instructor, she offered some tips on what to put in a sidebar.
Sometimes editors will ask specifically for sidebars, and will include that content in your word count (clarify this before you submit your article). Check out some back issues of the magazine to see the other sidebars they've printed.
As you know, I'm a big fan of Top 10 lists – and that is exactly the type of thing that makes for a good sidebar. And in some cases, your Top 10 list might be the inspiration for your longer article (I'll be writing about that topic next).
A good sidebar MUST be relevant to the story. Often it's a list of tips or resources from the expert author (that's you!) or an expert you interviewed. You could also use quotes (famous quotes or quotes from your interview subject), a quiz or statistics/facts about the topic of your article.
Sharon's suggestion: If content is important enough to include but will interfere with the flow of the story, move it to a sidebar instead.