I don’t think you’d be better off going to a small local retailer here @BendikHa. Probably much better off going to a discounter like Lidl or Aldi and pairing that with a cashback card or some that gives you some other benefit.
For Lidl I think the best pairing would probably be promotional Amex intro 5% cashback on the daily cashback card. (Assuming you can get one of these)
Either that or a 0.5% cashback card with a curve introductory 1% cashback added on top.
Thing is in the UK everywhere is expensive and that’s why these German discounters are becoming powerhouses
But yeah I guess for my tip: abuse a mix of credit cards, discounts and promotions.
Another tip: eat less. Go to Japan and look at their portions, they have the most people over 100 and that seems to be partially linked to their self imposed calorie control of around 1800-1900 a day in Okinawa.
That means you can get away with buying 600-700 calories less a day