Which extracurricular should I write about for my college applications?

This essay can be an elaboration/extension of a hobby discussed/mentioned in another essay if there is additional information to convey. In fact, that's how I read the question. What do you plan to major in? Identify to yourself the factors that make one successful in that major and pick an extracurricular that lets you discuss those qualities. It's better to write about something you're really good at or did something unusual in regard to. Show how it prepared you to be successful in college: you learned something new on your own, you worked independently, you were creative (thought outside the box) somehow, there was a challenge of some sort at which you excelled. Think of the skills and personal attributes that lead to success in college, and get them in your essays: work independently, devise solutions to problems, balancing demands on your time to accomplish all that needs to be done, keeping balance in your life, seeing a project through to the end, applying knowledge and skills from one field/experience to another. Make sure you apply all the rules about writing a well organized, thoughtful essay.

I'm not sure what GSA is, but I would use work experience.

I definitely would NOT use Pokemon Club. Unless you make an unbelievable essay about it, this would misrepresent your priorities.

Don't list Pokemon Club, or babysitting. Post the others and you should be fine.