Some mental tricks that can save you money:
1) Lots of research shows that paying through cash makes you think twice before you buy anything. In contrast, paying through credit card seems to increase unnecessary expenses.
2) When paying with cash, keep big bills with you and some small bills. This will help you in curbing the urge to buy small unnecessary things because it is relatively difficult to buy an Rs 50 item with Rs 500 bill then with Rs 100 bill.
3) Whenever going for grocery shopping, eat something before leaving home. You tend to buy expensive, ready-to-eat items when hungry.