After a wreck your body may hurt, your head may spin, your adrenaline may flow like a torrent. Your bike may be a tangled mess too, but that may be the least of your concerns. Perfectly understandable. However, you should do whatever possible to preserve your bicycle following a crash. The damage it sustains may reveal a lot about how the crash happened should you need to bring a claim or lawsuit against the at fault driver.
Time and again I have heard drivers and their insurers claim that a bicyclist "just crashed head-on into the side of my car/truck/whatever." Time and again a look at the damage to the bike undermines the driver's story and supports the bicyclist's recollection of events. In one case, an alleged witness to a crash claimed that a bicyclist ran head-on into the side of a vehicle, "T-boning" it. Were that the case, one would reasonably expect the front of the bike, the wheel and fork, to be damaged. However, only the rear wheel sustained damage, undermining the witness's recollection. In another case, another driver claimed that another cyclist smashed head-on into the side of his car. Yet, assessment of the bike's damage revealed its steel fork to be bent not backwards but to the side, supporting the bicyclist's account that the front of the car crashed into the side of her front wheel. Having a witness that supports the defendant driver's version of events obviously presents a challenge to the cyclist's claim. However, the bike itself may have a lot to say too, its damage providing the kind of hard, physical evidence that can persuade a jury that the cyclist is telling the truth.
Following a crash a bicyclist will generally have two opportunities to make sure that the bike is preserved. The first time will be at the scene. When the police arrive make sure to tell them to save the bike if you are to be transported to the hospital. As soon as you are well enough to do so, pick up the bike from the police station. At that point you will either bring the bike home or take it to a bike shop. In either event, photograph it. Ideally, you should avoid having the bike repaired, at least until you have retained an attorney who can inspect and photograph the bike himself/herself. But if you really need the bike fixed quickly at least make sure you tell the bike shop to save all damaged parts that they replace. Make sure the shop gives the parts back to you when you pick up your bike. Keep them safe, they may help you prove your case later.
Your body will be -- and should be -- your first concern after a crash. But keeping your wits about you and remembering to preserve a record of how your bike looked after a crash will help in the long run if a claim or lawsuit must be brought.