Toppers Booklist for UPSC
Prelims book list
Polity - Laxmikant
Economy - Sri ram IAS book on economics
Environment - Shankar ias book
Geography - 2 NCERT of class 11 + Vajiram handwritten notes
Ancient history - RS Sharma NCERT
Medieval History - Satish Chandra NCERT (for ancient and medieval, i didnt do these as my optional was history)
Modern history - Spectrum
Culture - Class 11 NCERT + Nitin Singhania (Book)
Science and Tech - Vajiram hand written notes
Current affairs - Vision monthly magazine + do extra modules from any institute for environment, economy, S&T current affairs
Mains book list
GS1:
History, Culture, Geography - same sources as above
Society - Society NCERT + internet research on topics in syllabus + Mains365
GS2:
Polity - Laxmikant + Mains 365
Governance - vision value added material + Mains365
IR - Mains365
GS3:
Economy - same as above + Mains 365
Agriculture, PDS - internet research for basic understanding of topics + Mains 365
S&T - same as prelims list
Disaster management - Forum compilation on Disaster management
Internal security - Internet/Vision value added material+ Mains 365
GS4:
Lexicon + examples from GS syallbus, personal life
Case studies - practice from booklets in market
Note: This isnt the only Booklist that you must follow. This is what i followed. You can choose material according to your own convenience (for e.g. someone may find Mrunal sir's economics better - that is upto you). However, your resources must be limited and must be revised again and again to gain maximum results.