Six Easy Pieces is just a few of his lectures pulled out of the famous volumes. If you already have the series you don't need this small book.
Stewart's is a standard reference for first year calculus. By the end of this course, you should be able to do all problems in the book.
If you are interested in having learned some material before class even starts, then it is a matter of getting a book in that subject and going through all the problems.
For more fun books, here are some that I think are interesting for math and physics: The Code Book and Fermat's Enigma by Simon Singh, The Drunkwards Walk by Leonard Mlodinow, The Quark & the Jaguar by Murrary Gellman, Surely You're Joking Mr. Feynman by Richard Feynman, etc. All these books are fun to read and are not necessarily life changing nor do they even teach you anything on the actual material, but they can give you good insight on history, different things not covered in class, and give you an understanding of the big picture while you work out the details in a textbook throughout your education.