Snakes are most often hit by cars and attacked by dogs. Make sure the snake is not venomous. You can tell a venomous snake by the triangular shape of the head, and the slit shape of the eye.
If you have a pillowcase, and wearing gloves, coax or put the snake in the pillowcase and tie the open end. Take the snake to a wildlife rehabilitation center that is licensed to treat reptiles.
Turtles often times are struck by cars as they attempt to cross a road to find a nesting site. If you find an injured turtle you will need to contact a wildlife rehabilitation center that is licensed to rehabilitate them. Most importantly you will need to write down the exact location you found the turtle, so that once it has been treated, and is ready for release, it must be returned to that area. Otherwise if it is not, it will spend the rest of its life looking for its home territory, and will not survive.
If you should find a turtle that is crossing the road, and is not injured, you can take the turtle to the edge of the road that it was headed towards. For a snapping turtle, use a limb or stick and coax it off the road. Do not attempt to pick it up by its tail or handle it. They can inflict severe injury.