Tell him to grow some veggies in the back garden.
You could buy things like herbs and spices, rice, noodles, puppodums, lentils etc (if you use any of those) from an asian supermarket as they are lots cheaper (go once a month or even less - just buy in bulk). They have things like big tins of tomato puree which are great for bulk cooking (doing a double batch of spag bol for example - use double the meat, add a couple of carrots, half a courgette, pepper, handful mushrooms, brocolli stalk etc all whizzed in food processor - and you'll have 2 extra dinners to freeze, not just 1).
Buy things like potatoes in larger bags (I find a 10kg bag is only slightly more than a 5kg bag - and our family of 3 would use that easily in 3-5 weeks, spuds last way longer than that!).
Buy veggies when they are on special and freeze them. Saves money and also time (freeze them ready to use). I particularly like to grab the Aldi super 6 (well, whatever is on that week that we'd use) whenever I am near an A store.
Frozen veg are great too.
For things like pasta, tinned tomatoes, flour, etc - buy the valu brands or go 1 level down from your usual - you save loads and really don't notice. I tend not to go down on certain things like tea, bread, biscuits, butter, meat.
Veggies and meat can often be cheaper and as good or better quality from local butcher and fruit and veg shop. Buy seasonal. Butchers often have the cheaper cuts that supermarkets don't necessarily like to carry (and which can be sooooo tasty - long slow cooking can make very cheap cuts divine!!).
Make sure you use up all leftovers.
Use loyalty cards for every store you frequent. Use coupons on things you'd buy anyway. Check out the special offers in stores before you decide the weekly menu and, when you can, shop around. One week the balance miught be for Morrisons, then next for Sainsbugs - or only buy your Sainsbugs favourites once a month and go to Aldi or Lidl once a month and Morrisons in between. Perhaps do your "dry goods" shop every 2 weeks only (or less often if you have storage space), which is a big shop (tins, packaged foods like pasta, cleaning things, etc...), and in between, go to local butcher, veggie man and a small shop in local store or different chain SM.