First, keep doing whatever you're doing to stay at the top of your class. Even without internal ranking, everyone knows who the top people are and word spreads. Then there's also the matter of actually needing to know the things you're learning, which you will in one way or another. So keep up the good work.
Research is far and away the most valuable addition to your schedule. Publications are one of the few things from medical school that will still be on your CV in ten years, and they are very valuable for top residency positions. Ideally these would be specialty specific, but that's not always easy to do unless you already know where you're headed.
Shadowing is a great addition if you are still looking for a career path. Spend time in any field that interests you, especially ones that are outside the core clerkships you'll do. If you find one you like, that can help guide your research and other activities.
You're wise not wasting time on step studying right now, but do have an eye toward that horizon. For me that meant experimenting with various resources and seeing what worked and fit my style. Personally I liked Firecracker and made keeping up with the flash cards part of my routine. There are far more resources now, but if you can incorporate some sort of spaced repetition thing into your study to aid in long term retention of material, it can't hurt. From experience, I can tell you it's awfully comforting to take your pre-study nbme and break 250. Not everyone is so fortunate, but you sound like you may also be the sort of lucky sperm who is.
Above all, stay humble and realize most people are really struggling. This took me awhile to internalize. Your friendships and relationships with others are also one of the things that will carry forward with you, so remember that you are lucky and do what you can to help others around you.
When it's all said and done, you and all your classmates will have roughly the same base of knowledge regardless of how easy or difficult it was for each student. As July 1st interns you will all be equally inept. Yet we know it's more nuanced than that. I think the most gifted students have this rare opportunity to float through all those stages unscathed by the dehumanizing and demoralizing forces that tear down so many. If you happen to be one of those rare few, you really have a duty to become the sort of kind and compassionate physician that everyone else will wish they could be.
