How do I know whether to upload a resume and what to put on it?

Answered

Generally, the rule I've always followed around resumes is that, if they include important aspects of your experiences or profile that you can't reasonably fit elsewhere in your application, then you should submit them. If not — i.e. if you can fit all of your info neatly into your Activities List and Additional Info section (which is where I would put those less important activities if you already have 10 on your Activities List) on the Common App — you shouldn't submit them unless a school requires you to.

I would mention though, because it's unclear from your question, that you should always fill up your Activities List no matter how "insignificant" an activity might feel. If you have more than 10 items and you need to cut some out to fit the more important ones, that's fine; if you don't have ten, you should absolutely use those small additional activities to get yourself up to 10. Honor Societies can also go on the Awards list.

If a school does require you to submit a resume, I would not leave anything off of it. It should be a comprehensive account of all the things you've done in high school, and even if it's redundant with your Activities List, it should put your most important activities front and center. In the most ideal scenario, a resume is something an admissions officer can look at a few days after they read your application to quickly refresh themselves on your activities and profile, so it should include everything relevant to that on it.