Our shopping bill has gone up with lockdown inflation, and also with my low carb diet. My husband lost his job at the beginning of lockdown, so it's been really important for us to budget. He follows a fairly normal diet, likes his carbs, and wouldn't be fully on board with low carb. However, I've managed to tweak things a little.
I eat two meals a day, so I don't have breakfast. He's quite content with toast for breakfast, so that's a fairly cheap option. Lunchtimes for me are mostly egg-based, sometimes ham, mushrooms, or whatever else I can throw in. I love sauerkraut, so that's usually part of it too and I've found it's much cheaper to buy the foreign brands than the supermarket own brands. Dinner is always low-carb based - we eat a lot of chicken, a small amount of beef, and some minced lamb - but we're both fussy, so we don't really have anything else. I buy "imperfectly perfect" veg from Sainsbury's, and a bag of potatoes for my husband... which I just bulk up his meals with.
We spend £70 a week, and I do shop at Sainsbury's (because I'm lazy, and Lidl/Aldi are not convenient). Around £20 of that is snacks/carbs etc for my husband, and £10 is food for Her Royal Poodleness.