How to hit two object with one raycast?

Use Layers to selectively choose what colliders a RayCast should detect.

If you need to check the plane first then the world, have a first RayCast layer set to the plane first, then fall through that if statement to another Raycast that is layermasked to ignore the plane, then use that collider info. An example from the docs. To ignore a layer, Check this link, scroll down to Casting Rays Selectively :

http://docs.unity3d.com/Documentation/Components/Layers.html

 // JavaScript example from the docs :
 function Update () {
   // Bit shift the index of the layer (8) to get a bit mask
   var layerMask = 1 << 8;
   // This would cast rays only against colliders in layer 8.
   // But instead we want to collide against everything except layer 8. The ~ operator does this, it inverts a bitmask.
   layerMask = ~layerMask;
 
   var hit : RaycastHit;
   // Does the ray intersect any objects excluding the player layer
   if (Physics.Raycast (transform.position, transform.TransformDirection (Vector3.forward), hit, Mathf.Infinity, layerMask)) {
     Debug.DrawRay (transform.position, transform.TransformDirection (Vector3.forward) * hit.distance, Color.yellow);
     print ("Did Hit");
   } else {
     Debug.DrawRay (transform.position, transform.TransformDirection (Vector3.forward) *1000, Color.white);
     print ("Did not Hit");
   }
 }