First priority is to avoid differentiating yourself in a bad way, so make sure you're squared away academically and comfortably passing. If you are able to do so, consider really pushing yourself and aiming to be the top student in the class or near to it. Often schools maintain internal ranking and things like AOA may be partly derived from it. But you absolutely must have your academics settled before even considering devoting time to anything else. If you start flunking classes or - god forbid - flunking a step exam, then you're really screwed. So don't differentiate yourself in a bad way.
Beyond that, I'm afraid to say that in the current model, research is king. This is not only because you get pubs, but also because it leads to close relationships with faculty and stronger letters.
For now, your best move after solidifying your academics is to figure out what you want to do. If you really want to do rural family medicine, then you can more or less hit the easy button and match well and be just fine. If you develop a love of orthopedic surgery or dermatology, then you have more work ahead of you. If you can pick a field early, you'll have more time to build a strong application compared to those who discover the field halfway through their 3rd year.
But then, you're going to have to suck it up and do some research. No way around it. Even if you're service or public health oriented, you'll need to have something tangible to show for it. A friend of mine did incredible public health work in sub-saharan Africa, wrote it up and presented it at the WHO -- now that kind of public health work would be noticed. But he also published multiple papers about the project in the research literature. In reality, it's much easier to bang out some chart reviews than it is to do meaningful work in service or public health.
