We also struggle to keep food bills down and it definitely takes laser-like focus. The moment I get a bit casual about it... BHAM, it screeches up.
A few things I think make a big difference:
Much as I love a rice or grain pouches, buy packets and cook your own. My 500g of rice today cost 85p and will do three of us for at least two meals and normal appetites probably 4. Pouches are at least £1 EACH and we'd need two just for one meal around here.
we also need the protein here but I do try really really hard to ensure that the protein is a quarter of the plate at most and that we'r ebulking up with vegetables. So, if we have a stir fry, there's meat, yes, but SOOOOOO MANY veg too. And I like to see what veg are on special, of cheap because they're seasonal, because it's a great way to bulk up veg. Eg I buy some form of cabbage most weeks to go in stir fries or other things.
I think pasta sauces are brilliant for this too - if I make sausages and mash, I'm looking at 3-4 sausages each for DH and DS. If I do a sausage based pasta sauce, I can do 4-6 for the three of us. And pasta itself is cheap.
Also, bulking out things like bolognaise with red lentils and extra veg adds to the nutrition, and reduces the reliance on the mince.
Most of the bigger online retailers do deals on meat/fish - 2 for £10 or 3 for £12 or whatever. I often browse those and get things we love when they're on those deals. eg salmon which is usually insanely expensive but is often on those deals - so still not CHEAP, but not AS expensive.
I use Amzon Fresh quite a lot for basics - they often have deals or their base prices are closer to what a deal price would be at a major retailer.
For oils, when olive oil prices went through the roof I switched to organic rapeseed oil for most things and just saved the good extra virgin olive oil for actual salads and dressings.
we do buy sparklling water but keep tap water in the fridge. we use cans of fizzy drinks because we don't drink them a lot but if we're having friends over or the kids are doign sleepovers, I do the big bottles as they're much cheaper.
Cheese is a nightmare but I found online, again, there's almost always a deal on cheddar. And we use cheese for vegetarian meals so that can get a bit pricier, but probably still cheaper than meat for the equivalent meal. For three of us, we do need 1.5 halloumi blocks which always annoys me as I then have to find somethign to do with the other half so it doesn't get wasted, so it's a regular meal when Ds has friends over!
I often use dto get good cheese deals at Aldi and LIdle too - but haven't been there for a while.
Cereals are a LOT cheaper at Lidl/Aldi. Try their versions and only go back if the taste is notably different!
This thread is reminding me that I really need to get back to Lidl. I used to do one big shop there every 2 weeks or so but I haven't done it for ages.