Don't buy bread, buy value strong white flour and make soda bread, you don't even need yeast and it's really quick to make - no need to wait for it to rise. This recipe doesn't even need buttermilk/milk & lemon juice
Irish Soda Bread
Combine:
4 cups flour
1 tablespoon sugar
1-3/4 teaspoons baking soda
1/2 teaspoon salt
1-1/2 cups water
2 teaspoons cider vinegar
Stir; it very quickly becomes dough. Form a round loaf. Place on greased baking sheet. Cut slits in top. Bake 40 minutes at 400° F. Best eaten the same day but you can sprinkle it with water and pop it back in a warm oven for 5 minutes to refresh it the next day if it's a bit dry.
Cheap vegetable soup, add porridge oats to bulk it out very cheaply. Oats can also be added to most curries/bolognaise/sauce based dishes.
Tomato pasta - saute an onion, add a tin or two of tomatoes, any dried herbs you may have (oregano or rosemary or basil etc) allow to reduce and then add a spoonful of cream cheese, serve with pasta. Tesco & Sainsburys value cream cheese is about 45p for 200g and tastes just as good as Philli for less than a quarter of the price.
Potato pie - boil potatoes and a finely diced onion together, drain, mash, add a little milk, butter, an egg and season. Top with breadcrumbs and a little cheese, pop in the oven for 20min. You can also add finely ham if you had any or stir some tinned tuna through. Really tasty, filling and cheap.
Spicy tuna pasta - good slosh of olive oil (assuming you already have this in your cupboard), slice and saute a red onion, add a tin of drained tuna, pinch of chilli flakes, pinch of dried mixed herbs, mix through to heat, serve with pasta (reserve a couple of spoonfuls of the pasta water to loosen the sauce).
Spanish omelette - finely chop any veg lurking in the bottom of the fridge (frozen veg would also do), saute, add a couple of eggs beaten with a dash of milk and season.
Buy whole milk - you can water it down if necessary to make it go further and it still tastes ok, skimmed milk on the other hand is vile if you do this.
Buy cheap stewing beef and make a casserole, your frozen casserole mix would work fine in this, as would the tinned carrots etc. Serve with the above soda recipe. You can bulk up the leftovers with some more stock and a few handfuls of porridge oats the next day.
If you have to manage on next to nothing then I would say that potatoes, oats, pasta, tinned tomatoes are your friend. Your meals may not be a nutritionally balanced as normal for the next 10 days but it's not the end of the world as a temporary fix.
HTH