Calculus, M. Spivak (undergrad calculus)
The Higher Arithmetic, H. P. Davenport (undergrad number theory)
generatingfunctionology, Herbert S. Wilf https://www2.math.upenn.edu/~wilf/gfology2.pdf (enumerative combi done with power series)
generally wouldn't feel too bad about not finishing any of these
@alexthecamel people who finish textbooks are higher beings