Just to support this advice, I note many of the sorts of colleges you mentioned do not have a special IR or Political Science school, and do not admit by major, or at least not for IR or Political Science (which might be unrestricted majors in some sort of Arts and Sciences division). You are just going to be applying for what is known as “general admissions” to their college, or perhaps their Arts & Sciences division. And while you may state an interest in IR/Political Science, that is completely non-binding in such cases. Indeed, typically at those colleges you are expected to explore, and very possibly change your mind, before declaring a major.
And while their students are doing that, they are also participating in a wide range of non-classroom activities in college. Sports, including at the club and intramural level. Student government. Student publications. Charities. What are loosely called identity organizations. Fine or performing arts. All sorts of things just for fun. And so on. All this is a big part of the experience at these sorts of colleges, and so those colleges value students who will likely be enthusiastic participants in some selection of their non-classroom activities.
Since many of the great colleges at which to study IR or Political Science work this way, that is all the more reason not to worry about which ECs you pick. Instead, just pick things you love, things you value for themselves, and dedicate serious effort to making the most of those activities. Because then you will obviously be the sort of student who will do that all again in college.
And I would also very much agree it doesn’t have to be a long list either. Usually admissions officers say they really just focus on the first handful of activities you list, because they assume those are most indicative of your own priorities. And it really doesn’t matter which sorts of things you prioritize, because all that will happen again in college as people focus on a few things among the hundreds of things happening at that college. So, they are fine admitting one person who is big into athletics, another who loves a performing art, another who loves debate and student government, and so on, because there are analogs to all that in college too.
Or you can be the lacrosse captain who loves writing poetry in French. The science fair kid who helps out at the local homeless shelter. The kid who spent summers rock-climbing and birdwatching.
My point is just the very positive images any of that can create in the mind of an admissions officer do not need to be made up of a list of 20 things. It can indeed be more like two or three.
But seriously, just do what you love and value with dedication, and it will work out well.