Power
Uh…what do you think? It's pretty much #1 on the hit parade. Your finger can hover all day long above the red button if it wants to—see the end of the Academy Award-winning Dr. Strangelove for details.
However, be aware that the President doesn't have as much power as you thought he did when you were seven. They can't automatically pass a bill into law, they can't force other members of Congress to agree with them, and they can't make lasers shoot out of their wrists. (That said, if you can make lasers shoot out of your wrists, you instantly have a leg up on the competition.)
You can veto a bill, but Congress can override your veto with a two-thirds vote. You can nominate federal judges, but the Senate has to approve them. You can deploy military forces, but only with Congressional say-so. Etc. And this is the most powerful person in the country? Pshaw.
There's also the period of time that a President is a lame duck, which is basically the executive branch's version of senioritis. This is the time after his successor has been elected (i.e., you've been accepted to a college and have nothing more to prove at your high school) until the time that his term ends (senior finals).
As you might imagine, a President's motivation to work his butt off is at an all-time low. So you also may have the power to sit on your hands and do nothing for the last few months. Better start practicing for that.