MySQL "Or" Condition

Use brackets to group the OR statements.

mysql_query("SELECT * FROM Drinks WHERE email='$Email' AND (date='$Date_Today' OR date='$Date_Yesterday' OR date='$Date_TwoDaysAgo' OR date='$Date_ThreeDaysAgo' OR date='$Date_FourDaysAgo' OR date='$Date_FiveDaysAgo' OR date='$Date_SixDaysAgo' OR date='$Date_SevenDaysAgo')");

You can also use IN

mysql_query("SELECT * FROM Drinks WHERE email='$Email' AND date IN ('$Date_Today','$Date_Yesterday','$Date_TwoDaysAgo','$Date_ThreeDaysAgo','$Date_FourDaysAgo','$Date_FiveDaysAgo','$Date_SixDaysAgo','$Date_SevenDaysAgo')");

Use brackets:

mysql_query("SELECT * FROM Drinks WHERE email='$Email' AND     (date='$Date_Today'      OR date='$Date_Yesterday'      OR date='$Date_TwoDaysAgo'      OR date='$Date_ThreeDaysAgo'      OR date='$Date_FourDaysAgo'      OR date='$Date_FiveDaysAgo'      OR date='$Date_SixDaysAgo'      OR date='$Date_SevenDaysAgo'    )");

But you should alsos have a look at the IN operator. So you can say ´date IN ('$date1','$date2',...)`

But if you have always a set of consecutive days why don't you do the following for the date part

date <= $Date_Today AND date >= $Date_SevenDaysAgo

Your question is about the operator precedences in mysql and Alex has shown you how to "override" the precedence with parentheses.

But on a side note, if your column date is of the type Date you can use MySQL's date and time functions to fetch the records of the last seven days, like e.g.

SELECT  *FROM  DrinksWHERE  email='$Email'  AND date >= Now()-Interval 7 day

(or maybe Curdate() instead of Now())