I only ever buy household products when on special offer. Especially, toilet roll, kitchen roll, Ariel, softener, bin bags, dishwasher tablets. Same with toiletries like shower gel, toothpaste, hand soap, deodorant, shampoo etc. I will sometimes visit 3 or 4 different supermarkets per week to stock up.
Also, Casino is good for meat offers. If you go early evening or Saturday afternoon they often have meat marked down by 30% if it has a short date. Last week they had Label Rouge chickens, originally priced at 4.95€ per kilo marked down by 30%. Had the following day’s date but we jointed and froze them the same day. Often find steak hachee and sausages as well.