Lots of threads on this topic. Some divergence of views, but a prevailing consensus that it's nothing like pre-med.
My take tends to be this:
1) Research is the most important EC, and by research I mean publications. One of the few things from medical school that still goes on your CV later. Publications are academic currency ($), so start earning some as soon as you can.
2) Beyond that, do things you actually care about. No since EC or even group of ECs are going to be make or break things for you; nobody is counting EC hours or leadership hours or whatever.
HOWEVER(!!!), you don't want your CV to be the only one that's 2 pages long! Have something to show for your time. Anything. Do things you care about since there's no bonus points for sheer numbers, but find ways to serve and involve yourself according to your own interests. I was involved in arts and music because that's my jam. I was on a couple committees for things I really cared about, was part of and helped lead a couple student groups, again for things I cared about. Had some involvement and work outside of school as well.
So nothing like pre med, but do more with your free time than Netflix.
Now back to Ozark....