I generally tell people to get involved with things that matter to you. Good both for your CV as well as your own mental health, but it’s not really part of the “game” like it is for Med school admissions.
I do make the caveat that having no ECs at all would make you stand out in a negative way, even with strong numbers otherwise. Most people end up with quite a few just by accident and being willing to get involved and help out as things arise.
Definitely keep a CV on your cloud drive of choice and keep it updated. Whenever someone asks you to be a part of X or help out with Y, put it on your CV so you don’t forget about it. Even without trying you’ll end up with quite a list after 4 years!