2D Movement Feedback

I am currently working on an Asteroids type project and would like to feedback on how I am doing movement. It is a 2D setup with a fixed camera.

Up increases thrust while Left and Right keys rotate the players ship.

I also use Drag in order to prevent a player from just moving forever.

void Update () {

    float amtToThrust = Input.GetAxisRaw("Vertical");

    transform.Rotate(Vector3.forward * -1 * Input.GetAxisRaw("Horizontal") * TurnSpeed *Time.deltaTime);

    //Just checking if the thrust control is on
    if(amtToThrust > 0)
    {

        if (current_thrust + Time.deltaTime <= max_thrust)
        {
            current_thrust += Time.deltaTime;
        }
    }
    else 
    {
        current_thrust = 0;
    }

}

void FixedUpdate()
{
    gameObject.rigidbody.AddRelativeForce(Vector3.up * current_thrust);  
}

This seems to work, but is this the best way to go about it?

Looks fine to me. Here's a slightly cleaned up version of your Update() function (not compiled or tested):

void Update ()
{
  transform.Rotate(
        Vector3.forward *
        -Input.GetAxisRaw("Horizontal") *
        TurnSpeed *
        Time.deltaTime
    );

  if(Input.GetAxisRaw("Vertical") > 0)
  {
        current_thrust = Mathf.Min(current_thrust + Time.deltaTime, max_thrust);
  }
  else 
  {
    current_thrust = 0;
  }
}

One observation I'll offer is that applying a thrust will generally result in acceleration (rather than an instantaneous change in velocity), so you might try it without the gradual increase in force and see if the results are acceptable (that is, just make the thrust 'on' or 'off', essentially).