OP you'll get lots of meal suggestions here but the easiest option for stretching a grocery budget is ChatGPT. Plus you don't have to deal with AI's opinions the way you do Mumsnet!
I input what ingredients we already have in the press (this is the tedious part), where we shop, what our dietary requirements are, what our macro needs are, what our food preferences are, and ask for a meal plan. I ask to approve the meal plan before the chat sends me the grocery list, so I can make any tweaks.
So a good prompt would be "we are a family of four, who need a cheap, nutritious meal plan to do until the months end. Our family is comprised of mum (height X, weight X, activity level X), Dad (height X, weight X, activity level X), and active children age X and X. The meal plan must include 3 meals and 2 snacks a day. Dad must be able to pack his lunches for work, DC must be able to pack them for school.
Our monthly budget is X. We cannot go over this.
We like eating X. We do not like eating X. We have X dietary requirements.
We have X and X in our press or freezer already.
Please suggest a meal plan, and accompanying grocery list. Please wait for the meal plan to be approved before sending the grocery list. Break the grocery list down by category of food.
You can also add photos of your previous receipts to ChatGPT and ask it to suggest savings.
Personally when I'm on a budget, I find click and collect shopping easier as I'm in more control.