What can I do NOW in college to prepare my hands for surgery when I am in medical school?

Your time would be better invested elsewhere - dexterity can be built up later on. For example, you could volunteer in a hospital, deliberate entering medicine in the first place (this should never be an easy and clear-cut decision), learn scientific principles, or work in caring environment, such as hospice. All these activities are far more relevant.

Work with a stress ball and keyboard typing exercises. This will strengthen your fingers and agility of them. Also maybe pick up sewing/knitting, as Ive heard it helps as well.

My mom roomed with a surgical resident who would carve bars of soap into all sorts of beautiful things.
Play piano. It's great for strengthening fingers and promoting good posture.
Learn to sew, particularly very fine needlepoint.
Practice knot-tying and fly-tying. You can practice while you fish! (now, that's multitasking)
Do anything which requires very fine eye-hand coordination. Small sculptures and calligraphy are very "fine motor".

The skills that a surgeon needs are less in the hands, and more between the ears. Short of keeping your hands away from lawnmower blades and sharp knives, other things aren't going to make a bit of difference.  Really.

Any monkey can be trained to perform surgical procedures.  It's knowing what to do when, and when not to do anything at all, that is more important.

Lay your hand flat on a piece of paper and draw an outline around your fingers.  Then move your hand one 'finger' over and draw a 6th finger.  Then move it back two 'fingers' and draw a 7th finger.  Then ball your hand into a fist and extend one finger at a time and practice touching it's original position and the position to its right and left.  If it's too hard at first, try keeping your hand about a half inch above the paper and touching each space.

Although you can demonstrate it to your self now, you'll have to relearn this skill once you're in residency and that's controlling your fine motor movements.  Hold your hand about a foot in front of your face in a well lit room.  Pick an objective in the distance and align your hand to it.  Notice the movements your hand makes, especially when you breath.  If you were holding an instrument under a microscope those movements would equate to swinging your arms to the extremes of their movements.  To learn to control these movements, avoid all caffeine products and don't lift anything over five pounds.  Take a pen or pencil and make a small dot on a piece of paper.  Then hold one piece of uncooked spaghetti in your hand with the end on that dot.  Rest your hand comfortably on its side and keep the end of the spaghetti on that dot.  If you can keep it on the dot for five minutes, you're doing good.  Once you reach that point, lift the noodle about a centimeter off the dot and try to keep it still.

Once you get into a surgical residency you'll be taught other techniques.  One of the most difficult is learning how to suture.  The closest thing to that is building rigging a model ship inside a bottle.

Given the trend toward laparoscopic and interventional radiology procedures, I would suggest video-games.  Research has supported this practice and some residency programs provide video-games in resident lounge based on this.

Despite what comments above may say, hand eye coordination, strength and dexterity are very important in surgery.  Not anyone can be trained to be a good surgeon.  There is innate ability involved, which practice can improve upon- but not everyone can be a good surgeon despite unlimited practice.

In addition to hand-eye coordination, dexterity and all the rest, your perceptual abilities are really important. Practice those skills as well. You also need to have a "light touch".  That determines good outcomes too.