A lot of schools don't really ask for proof of your work. While I was applying, I think only WHU ever asked me, and that was an anomaly. I would recommend bringing out your work experience and volunteer work really well through your CV and essays. Especially in your essays, where you can really focus on the work you did and the value you added or skills you learned.
I added my Coursera course certifications in my CV and did mention them in some answers or essays, if I felt they helped my case. What really matters is that you point out your interests and show a certain direction, rather than just list down everything you've done. For example, if you've taken out the time to do a Digital Marketing course, you would want to explain how that falls in line with your ambitions and the general goals and direction of your career.
As for the gap year, I think as long as you have been adding value in any way (courses, volunteer work, etc), it's not a problem. Volunteer work is actually a big plus, if I'm not wrong. My GPA was also a tad below 7, and most Universities give you the chance to explain your score, and the reasons they don't represent your academic capabilities, if you feel they don't. A great GMAT score here helps to back that statement, of course.
Hope this will be helpful!
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