How does one prepare for a big chess tournament? The Chicago Open is in four days. Assuming a player continues his daily regimen of reading chess books for a few hours and playing two, perhaps three slow games (60/5, at least) a week, what else should a player be doing?

Also, should a player stop this regimen before the tournament to "clear the mind"? If so, how many days before?

Regarding openings

I'm completely confident in the middle game. Everyone says that opening study should be reserved for when I'm higher rated (~2000).

This is true, because by following general strategy, I can transition into the middle game easily. With a plan, it's hard (if not impossible) to go wrong.

Why, then, does everyone advise to review openings before a tournament? (I have taken perhaps a brief look at the classical variation of the Ruy Lopez, but that's it.)
Eat your carbs, get up at a time such that you'll be most alert during the games, maybe play a few blitz games to go through your opening repertoire. Move around according to your level of physical activity, because you're going to be sedantary for a long time.

Playing long, proper games is exhausting if you're really focused throughout, so you don't want to play any extra games just before the event. Reading chess books at a time so close to a tournament has its parallels with cramming before an exam: it pays off if you're faced with something relevant, but could cost some precious mental energy.

Be rested and stop training long enough so that you feel ready on the day of the event. For some, one day is enough, others may need over a week.

On an indirect note, fatigue usually starts to set in after 4 rounds or so; physical endurance is actually important here. While it's a little too late to address this now, if you find yourself making incredibly careless mistakes in the later rounds, you'd want to consider adding a physical part to your regime if you're serious about the game.