In addition to the above, would also add: find a way to go see some patients who are presenting with surgical emergencies, and put your hands on a real surgical abdomen; then go scrub that case and see how it plays out.
Learning to sew and tie can be useful as you may need to stitch up some simple lacs one day
Getting comfortable with sterile technique since this will apply to all the procedures you'll do in IM
Jump at any chance to perform simple procedures you might also do in IM: central lines, chest tubes, a-lines, LPs, etc.
I'm sure I'll think of more.
Basically, just get in there and do/see as much as you can. You'll spend your career making referrals to surgeons and taking care of patients after surgery, but this may be one of your last chances ever to see the inside of an OR. Try to get some OR time in as many surgical fields as possible and see all the most common procedures in each.