The gun, the ammo, boots, shoes, hunting clothes, ATV, gun case, everything. Don't throw ANYTHING away.
Get a copy of any law enforcement report. Don't despair if all of the facts don't mesh with what you think happened. Law enforcement's first goal is to determine whether the matter is a criminal matter. If it is not, some law enforcement don't do a complete investigation.
If you are the victim of a hunting accident, don't think about sections one and two until you get the best health care that you can. Go to a bigger city if you can, especially if the injury is serious.
Hunting accident litigation is often very complex. There are issues related to products liability, premises liability, personal liability, insurance, jurisdiction (state or federal), and a whole host of other issues. Do not hire an attorney who does not have extensive experience handling hunting accident cases.