In order to score good marks in BITSAT it is very important that your basics should be clear. You can take help from NCERT books to make your base strong. 

Apart, from NCERT you can refer below books

Physics

Concepts of Physics by H. C Verma Vol 1 and Vol 2

Understanding Physics Series by D. C Pandey

Chemistry

OP Tandon

Arihant

Mathematics

RD Sharma

For complete package you can refer A Complete Success Package for BITSAT by Arihant (with CD) or complete pack by Disha.

BITSAT is a speed test it is very important that you increase your speed by solving as many as mock test series.

All the Best!!