What are some good extracurricular activities for intended public policy majors?

Nice work on what you've already done! These things definitely sound applicable to a potential Public Policy major.

So, the thing is that colleges don't care so much what extracurriculars you do, as long as they demonstrate your genuine interests. Colleges care more about how devoted you are to your activities, and what you've achieved in them. If you're on this platform, I assume you've had some exposure to the Tier System. There's a great CollegeVine blog post on it, if you're not familiar with it: https://blog.collegevine.com/breaking-down-the-4-tiers-of-extracurricular-activities/. Basically, colleges evaluate ECs based on their "impressiveness."

At the same time, you should take care to balance the strength of your ECs with quantity of ECs. The most competitive candidates to schools like UPenn will have 8-10 ECs with at least a couple Tier 1 or 2 activities (this might sound like a TON, but keep in mind that most activities are seasonal). It sounds like you already have a bunch of relevant activities, so it may make more sense to try to achieve as much as possible within the ECs you already have (basically, try to push them to higher tiers through major quantifiable achievements). Colleges would rather you deeply develop fewer ECs than dabble in a bunch of them.

If you're not feeling good about the number of ECs you have, and want to do more public policy-related ones, take a look within sectors that interest you. If it's human rights, consider volunteering or interning for human rights orgs to get firsthand experience beyond the organizations you founded. If it's the legislative side of public policy, consider working as a state or national senate page. Basically, determine what specific parts of public policy interest you, seek opportunities in those, and try to achieve as much as you can within those opportunities.