I have space for 2 more ECs on the commonapp, and I’m not sure which would look best:
SCA treasurer, 2hrs/wk (11,12)
IB student council committee member 1hr/wk (10,11,12)
Babysitting 2hrs/wk? (9,10,11,12)
Self-Taught Classical guitar 3hrs/wk (9,10,11,12)
Self-taught esperanto 4hrs/wk (11,12)
1 month Lab internship, mainly involving benchwork, about 35hrs/wk (11)
My intended major is pre-med/molecular biology/economics/anthropology
Thanks!-
Assuming these are at the bottom of your list, it really doesn’t matter. Choose the ones you would rather be asked about/talk about, if that helps you decide. Which are more interesting/important to you? Don’t choose based on what you think LOOKS best.
Thank being said, make sure you have taken advantage of any groupings possible - i.e. if you have some listings that are similar (say, music-related), you can group them into one. Also, if you really feel you need to include more than 10, you can use the Additional Info section. But remember that if these activities weren’t deemed important enough to list as your top ten, they probably don’t need much explanation…a bullet-list of “additional activities” could work.
I would include the lab internship for sure, as that correlates well with your intended major. 
First and last one I’d say.