When you're in the academy one of the classes you may try to breeze through is first-aid. But this is also one of the most important to pay attention to for several reasons. The first of which is it could save your life or the life of a fellow officer.
Most of the academy students seem to think that when you get to a scene the ambulance will already be there with EMTs available to handle the trauma. This is so far from the truth it's almost funny. That's why you need to pay attention in class!
While you're at it, try to determine how you could perform self-aid. Many times you're going to be the solo officer on a call and you could become injured. What will you do until the ambulance arrives? Approach the course material with this in mind so you'll know how to react.
Don't think that because you are young and strong this will never happen. Such a mindset will get you into trouble. Most tactical teams are now teaching self-aid and buddy aid because they recognize the importance of such skills. They've learned this from the military and learned well. Remember, you need to get yourself back into the fight so you can keep the mission moving forward. People are depending on you.
Most departments will issue some first-aid equipment to you - a CPR mask and gloves at a minimum. Additionally, each vehicle will have some cookie cutter first-aid box in the trunk. But if you're relying on this, inspect it frequently, especially if you have fleet cars. It never fails; some officer will ride a crash and perform some first-aid and never replenish the supplies that were used.
I have always recommended to my students that they carry some of their own first-aid supplies (beyond what is issued); if not for themselves, then to aid fellow officers. A low-key suggestion is to carry in your briefcase a variety of sizes of plastic bandages and a small tube of antiseptic. You will get cuts on the job, so this will at least allow you to take care of them and yourself.
I also recommend that each officer carry large "battlefield type" dressing in arm's reach in the front of the car. These are cheap and easy to find (go to the military surplus or camping outfitter). I strongly recommend that you have a dressing with a hemostatic agent to be applied directly on wounds to stop bleeding. These agents work by absorbing water from the blood, concentrating the clotting factors. These should be available to you in the vehicle within arm's reach. Should you get into an accident or become severely injured on patrol there is a high likelihood you can prevent yourself bleeding out.
I have added a tourniquet to my car bag as well. Without getting into a major discussion about their application I suggest you talk to a returning veteran back from the Middle East. The military has reviewed this in detail with some dramatic results. Get some training on this; revisit the military surplus store to buy manufactured tourniquets for a few bucks.
You knew this was coming from me. Have some drills on how you would respond to an injury, and practice them.
You get to a position of cover; you attempt to simulate applying a dressing with one hand. How would you call this in via the radio? Every department has an officer in trouble signal and protocol. Run through scenarios covering all these important aspects and more to be truly prepared.
If you don't practice, when the moment arrives you will fall to the lowest level of training you have had, if any. A time of crisis is not the time to panic but to control your body, emotions, and what is around you. If you lose it, then count on going into shock or hyperventilation. Planning and training will give you the edge you need to perform under stress.
There are a thousand other things we can talk about but these few pointers should promote thinking and preparing your strategy to win the battles of life.
Train like your life depends on it.