I am a DO student and here is my story
I applied to approximately 20 programs(Mayo, RIC, Stanford, UCDavis, Emory, UofM, Wisconsin, etc) and received interviews to all programs except Harvard. I think that I may have received an interview at almost any program I applied to.
My grades for years 1 and 2 were usually mid/high 80 percent to low/mid 90s for classes but my school was pass/fail so that really did not matter. I was probably top 1/3-1/4 of my class
Comlex 1 86 percentile, Comlex 2 74 percentile (should have studied more)
I had also been previously accepted to PT school but declined, so that helped.
Being a DO can only help you in this field, I did not find any problem with my training where ever I interviewed and one allopathic program director said we were better trained for PMR.
During years 1&2 I participated in OMM Club, Sportsmed Club, IM sports, and various other volunteer activities. I also signed up for extra elective course in OMM, PMR, and Pain Management during 2nd year. During 3rd/4th year I rotated in Neuro/Pain/Ortho/Neurosurg/PMRX2/Sports Med. My PMR rotations were at major universities with programs and was able to receive rec letters from both of them.
I spoke with many residents from various programs way before the match even started. I joined AAPMR as a student member, for 50$/year you get the journal and another addition to the CV.
I did not publish or do any research during med school but had some from undergrad. Do you need it? No. Can it help? Definitely, especially if you are a weaker candidate.
Things I wish I would have done: Interviewed at more programs such as Charlotte institue of Rehab, and MCV, and possibly some more of the bigger names. You can easily do a poster presentation at a conference or your school's research day on an interesting case you saw during 3rd year.
I ended matching at my first choice; University of Wisconsin. I was looking for programs very strong in Outpatient/MSK but also with adequate inpatient training. I found UC Davis, Mayo, University of Wisconsin, and RIC to be the tops for what I was looking for and where I interviewed. Hope this helps, feel free to PM me with any other ?s
Good luck and it is never to early to be thinking and planning for your future because time does go fast.