ASA Commercial Oral guide ( paper or kindle) , Pilots Handbook of Aeronautical Knowledge, Aeronautical Information Manual (AIM) , ( both FAA, free download), the Gleim theoretical knowledge exam book, and a proper read of part 14 CFR part 61, especially the section on prerequsites for check rides, and part 91 ( eg 91.205 etc) Also- your own copy of the POH for the plane you will do your check ride in is a good idea.
And a TSA clearance if you don't already hold a FAA stand alone private. ( non 61-75) ...