A good place to start is the offers section, where you may find another brand of a product you regularly buy for much cheaper than usual. We try to look at the current offers available, and base my meals around those.
You might also want to try shopping for grocery items at a local market or store. Prices of commodities from local shops are actually much cheaper compared to supermarket prices, plus products are fresher. You just have to bear with a humid and hot atmosphere.