These things will help differentiate you, but they obviously are secondary to Step 1 scores/Research/Grades. Having said that, devoting a lot of time to...say.... the free clinic will probably help you in your 3rd year clinical rotations. Also, many times I've found ECs have helped me find what sort of things interest me particularly in medicine. And which don't. I'm a manager in the free clinic, do some work with the AMA (currently drafting an AMA resolution), and advocacy work for minorities in medicine. They keep me happy, but most aren't going to lead to any specific "publication". You should be keeping up with grades and classes, but to a certain extent....remember that medical school is also the time to start to carve out your role in our medical system and what sort of broader things you might want to do with your career. This could be women's rights, basic science research, health education, policy, etc. If you have the time to try things out, take advantage of it- you many find an issue or calling that fulfills your career.
I've actually found that in a few hyper-competitive specialties, students with some unique, very personal interest (related or unrelated to that specialty) end up doing better. Maybe this stems from the fact that (as always), people are looking for more than just grades. They look for people with genuine passions and who have the will to follow through with them.
Personally, I go to a P/F school and we have 9 weeks to study for Step 1. I also have found that (by now in my 2nd year) I've learned enough what resources are good for studying for exams and how to do so very effectively. I also realize that I forget almost everything about a 3 days after I take the exam. So, again, I'm not sweating over getting a 90%+ on everything. It'll "come back" when it needs to come back (i.e. starting 9 weeks before my board exam). Maybe my "activities" keep me more at the 85 percent tile on exams. But, I'm having more fun while doing it.
