You can do it. Set aside the formula and essential petrol money. Then go through your kitchen cupboards/freezer and see what you've got in. Not sure what your cooking skills are like.
If you don't have much in then this website do fantastic cheap meal plans if you sign up or follow the Facebook page.
https://fyf20quid.co.uk
Other ideas - does anyone local to you do Olio (app that you can get free food from)
Is there a community fridge locally?
Both of these are schemes to pass on excess food to stop it going to waste so are bit different to food banks and anyone can use them.
Breakfasts - porridge, pancakes, toast, cereal, dippy eggs
Lunches - soup, toasties, leftovers from dinner, omelette
Dinner - pasta, chili, spaghetti bol, cottage pie, stir fry, economy fishfinger, nuggets for little one
Treats - cheap biscuits, home baking - flapjacks, apple crumble, tray bakes, chocolate chip cookies etc
Swap to own brand, switch to Lidl or Aldi
Good luck you can do it. If this is a temporary blip then you will cope for one month. If you need to permanently reduce your expenditure on food then learning to meal plan and batch cook are the way to go.