Personally, I think when you're younger and have less actual stage management experience, it's ok to have some non-SM credits on your resume. If possible I would limit them to theatre experience- backstage positions you've held, etc. I would put them in a separate category on your resume than your SM credits.
It's also appropriate to include a (short) list of related skills- do you read music, speak French, are you First Aid certified, etc. My personal thought with related skills- make sure they are truly related! I always think it's kind of silly when people have a huge list of skills and none of them have anything to do with stage management. I also include a short Education section and References at the bottom of my resume.
When you're just starting out I think that it's okay to have a lighter resume- better than cramming it full of filler. Add experience as you obtain it, organize the experience you have in a clear and legible fashion, and as you're able to, phase out less-related positions, like run crew.
I would check out the Resume Browser to see examples of what others have done. If you're interested in having an outside perspective on your resume, send me a PM and I'd be happy to offer suggestions.