There is no requirement for any book other than study material provided by ICAI for those students who have studied Accountancy ,Economics and Mathematics subjects previously they can refer their class 12 books for concepts and for exam purpose there is no requirement of any other book than study material because the mostly paper comes from study material .
If one has not studied these subjects in class 12 then they should take coaching classes it would guide them and for concept clarity of Accountancy they can refer Accountancy book of D.K. Goel of class 11 and 12 and Economics book of Sandeep Garg for Class 12 only for concept clarity .
Mercantile Law should be studied from the study material only if one is finding it's language tough then they can take help from some other book like P.C. Tulsian or M.C. Kuchhal But again for scoring and passing in CPT study module should be read completely it will help students in IPCC if they start studying from study material.
For practice purpose and exam study material is recommended and no other book.