I use the a little different strategies:

• I choose to go to 1 supermarket with competitive price and got the membership which allows me to get discount. I level up this membership to highest rank and I get more discount and voucher
• I use the credit card which has the cashback and use it regular. I keep tracking the payment regularly to make sure there is no penalty because of late payment. Finally, I can get a cashback amount more than 3x of the annual fee. It's a gain for me.