I think that the best book by weight is Maxwell Quick Medical Reference (it's a small book with colored pages with all the info you need to write notes, including standard lab values, useful equations, etc.) You probably won't need to carry around any physical diagnosis books after the first week or so. Another little book that's a bit heavier but useful well into residency is the "Pocket Medicine: The Massachusetts General Hospital Handbook of Internal Medicine."
I really like the Lange "Case Files" series as well as the "Pretest" series for rotations. Some people like "Step Up to Medicine," but it's pretty long and heavy. Many people also like the "Blueprints" series. For pediatrics, I think the pretest and case files books are very good -- and if you can get a copy of the Harriet Lane Handbook, you'll know more than the residents ; )
I swear by used books, but I don't know how easy it is to come by new-ish used books in India. Otherwise it gets very very expensive very fast.
I am not sure what you mean by "final year" med student (4th year?) If you are just beginning your rotations, Boards and Wards is perfect. Everyone at my school and the surrounding Philly med schools all had one in their pockets (quick and precise reads in almost all subjects and a great resource for quick Step 2 studying while sitting around on rotations). If you are referencing specifically 4th year IM and peds, Washington Manual is critical (will absolutely use it as a resident). If you are planning to do residency Family Medicine or peds, I'd highly recommend Harriet Lane for peds. If not, Pediatric Secrets is a pretty good book but the only problem is that it is a bigger soft cover that cannot be placed in your pocket. Hope this helps.
"Cure sometimes, Care always" <br />Dr. Robert Fogel. <br />"Go confidently in the direction of your dream. Live the life you have imagined". HD Thoreau