Mock drill

Wordsmith.org defines tautology as the unnecessary repetition of an idea, especially in different words; for example, a good-looking beautiful woman. 

A few days ago I came across an example of it in The Times of India:
 
A mock drill was conducted at New Delhi railway station on Wednesday to check the preparedness of various agencies in responding to emergency situations.

A drill is an exercise, not a real emergency; mock means the same thing, so there is no need to add it.  

Here are some more instances:

• past experience
• major disaster
• repeat again
• free gift

There are many more which are equally common and have almost become fixed expressions which we use without thinking.