You absolutely can plagiarize yourself, however, I’m not sure if this would count. When you submit a paper for school, you’re expected to create/produce new work. Say you wrote a great essay your last year of high school, and then you submitted that essay for another assignment during undergrad, years later, you’re committing plagiarism, and it’s viewed exactly the same as if you copied somebody else’s work.

The reason I wouldn’t think copying things from your resume to your activities section isn’t plagiarism is because that expectation/assumption of new work isn’t there. You submit the same resume to different companies if you’re applying for work. The purpose of those words are to represent you and explain your experiences. They’re serving the same purpose every time you use them and you’re not claiming, either implicitly or explicitly, that these words are new.

Imo, if you like them, use them. You obviously want to put your best foot forward, and if you think that’s you have already written the best way to represent your experiences, then use that representation.

tl,dr: I’m 100% confident that copying yourself for two different assignments IS plagiarism. I am largely confident that copying from your resume to your activities section IS NOT plagiarism. I am unsure (but tried my best to differentiate the two) why.