Don't forget to also do a few mission trips to save babies in Africa and win gold medals in the winter Olympics in three different sports while you're at it. 😉
OK, so seriously, any of these suggestions (with the exception of mine!) would help your app, OP. But obviously that's a lot to take on at once. What I suggest is that you add ECs one at a time. First, start by making sure your grades are as close to straight As as possible. You're done with one semester now, right? How did that go?
If you're already acing all of your classes, you should next start looking for a lab to join either during spring semester or for this summer. Getting significant research experience is essential for someone who wants to do MD/PhD, but you shouldn't do research at the expense of tanking your GPA. It's very easy to take a year or two off during or after college to do research if you need more lab experience, but it's very hard to pull a low GPA up once you've started getting a lot of Bs or worse. So keeping your GPA up is your first priority, then research experience.
Once you've reached some kind of balance with your grades and research, then you can see about doing a little shadowing or hospital volunteering. You don't have to go crazy; just spend a couple hours per week in a medical setting where you're around physicians and patients. If you do that for one year, you should have plenty of clinical experience.
When it comes time to take the MCAT (generally spring of junior year for someone who is going to apply to med school straight out of college), make sure you prepare for it properly. Ideally you will want to shoot for a 35+ score if possible. But you can worry more about all of this a little later; for now, focus on doing well in your med school prereqs, which will in turn improve your knowledge base for the MCAT.
As for a publication, it would be great if you could get one, but don't worry if you can't. Publishing a paper would be a bonus for your app, not a requirement. The other things we've mentioned (grades, research experience, MCAT score, and clinical experience) are the most important and required components of your app.
Best of luck. 🙂