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would it be wise for me to leave out jobs that I worked "off the books", because 2 of my 3 major employments through my high school/early undergrad years were "off the books" so it would really diminish the "density" of my resume.

I am only asking this because when the bar does a background check, I don't want to look like I was lying about 2 previous employments on my resume that I submitted with my law school app.

You're putting way too much thought into this. Just put them on there if they are significant jobs. If they were little rinky dink jobs, then dont. Truthfully, your resume will not be scrutinized all that much. Schools just want to see something. They dont care if you only had one part time job throughout UG.

Good luck!