Admittedly 35 years ago, this was exactly my situation, as I had had my purse"raided" by the au pair of a friend I had visited while she was showing me round their new house. When I got home and went to pay the milkman, all the notes had gone and I had precisely £8 for the week. I bought eggs, bread, bacon, milk (but didn't have to pay for it until the next week, because delivered) some potatoes, I had butter/spread and a little cheese and I think I had or bought some sausages and maybe fish fingers. DD1 was 2 and DD2 was just a babe in arms. I made it to the end of the week as I also had pasta and tinned tomatoes in the cupboard, but given the price of eggs and bacon, not to mention sausages, I don't know if £8 would have done it.
I know it was the au pair, by the way as another friend had had exactly the same experience a few hours after me and challenged her. I never got my money back and was too embarrassed to insist!!
I now have so much in my fridge and freezer we could probably manage for a month.