I would go with invisibility. Time travel can mess stuff up.
EDIT: I'm glad this is back. Many memories in this thread.
						
					
					
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	Time travel. I would totally try to be Dr. Who, and save people! And stop wars! And probably die trying! [spoiler]But seriously, I don't have the right to say what would be good or bad to change in the past. My real answer is potato[/spoiler]
 
										 
					 
		    