Slow cooker or instapot type thing to make meals in.
Jugs of drinks seem to be more cost efective than seperate drinks.
Pan meals(lasagne, sheperds pie etc) or curries and stews.
One Pot meals help so much with both cost and time. Spagetti or pasta meals. Rice with chicke, Paella....
"Dish your own meals" like Tacos, burritos, wraps etc are cost efective and uick to prepare.
Shopping at lidl and aldi help with shopping bill. Even if you shop there only for staples and get treat items elsewhere, you can still save.
Look out for special offers.
baking cakes and traybakes can work out better than buying.
bulk buying really helps. Big bags of rice and pasta are so helpful.
Having some frozen veg on deck helps to make meals spread. Also nice as I often find fresh can spoil before I get to use and I hate waste.
If you can, get a chest freezer and take advantage of meat deals.
Look out for def in stores (yellow ticket in most) and freeze.
Having porridge instead of cereal on some mornings (oats, cornmeal, semolina are often quite low in cost and stretch for many "gos")
Beans and Pulses can be added to many dishes to bulk them up and also great for protein/health boost.
Have "take away at home" nights. Eating out with big families can be very costly, I often do these nights, The cost is often minimal and the kiddies feel like it's a treat.