Very generally, any and every document that you have obtained. I strongly recommend seeking representation as soon, as close after the accident occurs. At that point you might not have that much documents, but just specifically, any photos that you might have taken, or if you have taken pictures of the at-fault or the other driver’s insurance card, license plate, anything such as that or typically what’s provided.
Also, if you do go to a hospital immediately after the accident, sometimes they’ll give you discharge summaries as to indicating what your injuries were. That’s also very important to bring along as well, but basically whatever information you have gathered. That way the attorney can make copies, and they could have that for the file and then give you back the originals. It’ll just be more beneficial down the road.