A sample Unity camera shake script that works with the prefab first-person controller. Add this to the "first person controller" object.

CameraShake.cs

using UnityEngine;
using System.Collections;

public class CameraShake : MonoBehaviour {
	public float shakeStrength = 5;
	public float shake = 1;
	
	Vector3 originalPosition;
	
	void Start()
	{
		originalPosition = transform.localPosition;
	}
	
	void LateUpdate()
	{
		if(Input.GetKeyDown(KeyCode.Q))
		{
			shake = shakeStrength;
		}
		
		Camera.main.transform.localPosition = originalPosition + (Random.insideUnitSphere * shake);
		
		shake = Mathf.MoveTowards(shake, 0, Time.deltaTime * shakeStrength);
		
		if(shake == 0)
		{
			Camera.main.transform.localPosition = originalPosition;
		}
	}
	
	void OnTriggerEnter(Collider other)
	{
		if(other.gameObject.tag == "shake")
		{
			shake = shakeStrength;
		}
	}
}