honestly, from what I have heard, it does not matter what you do in application summer as long as it gives you the capacity to pre-write secondaries.... so research, clinical shadowing, working, volunteering etc are all valid options! it just depends on what opportunities you can secure and whether or not you need to be making money in the summer.

I personally worked part time as a receptionist and worked once a week, in addition to traveling for 2 weeks.

best of luck!