If you find a turtle during cool months, you do not want to warm it too quickly. Again, for only a few hours, put the box in a quiet room in your house. Do not handle these turtles except to take care of their needs. They see us as a large predator and do not realize that we are trying to help them. If the turtle is bleeding and you can safely do so, apply a bandage and tape it to the shell.
Sanitary napkins cut to size for larger wounds work quite well.
If you discover that for whatever reason you are going to have to keep an injured turtle more than a day and profuse bleeding is not a problem, you may soak the turtle in plain tap water for about an hour once everyday. This will allow the turtle to keep itself hydrated. Aquatic turtles with damaged shells should not be left in water other than for a daily soaking. Leaving them in the water allows bacteria from their stools to enter the wound and cause infection. Box turtles should not have free access to soaking water for the same reason.