I have £18 shopping money left to last me till the end of the month but my store cupboards are stocked with pasta and rice and i just need milk, bread and veggies. Try buying a couple of stock cupboard items whenever you can (BOGOFF offers etc) and putting them away for when you are really short. Not much help now but might help more going forward.
Speak to the guide leader, don't avoid her. She will understand and she might even be able to offer practicle help or be willing to accept a smaller payment in the mean time. Ask grandparents if they will help with the cost of guides too.
Is there a lone parent group near you? The chairlady at my local one keeps a stash of frozen meals in her freezer for situations like yours.
Also speak to the benefit people, you might be able to get a loan which can be paid back over a period of weeks.
Food wise try pasta and a tomoatoe sauce (tinned toms, a few veggies thrown in and then a little grated cheese or chopped up cooked sausage chunks for protein). Also stirfry veg with cubed potatoes chunks rather than rice, throw in some chickpeas for protein, or again chopped up sausages.
A little can go a long way. Beans on toast won't take much electric to cook either.
It's only a few days this time, but it sounds like you need to sort out a budget and forward plan a little more to help your cash flow. Do you have a computer with a spreadsheet? I have every penny that comes in allocated against bills, expenses like scouts, food, car running costs etc and I have to stick to my budget or i end up with no food money. Might help you see where you can maybe cut a few costs if you list everything out for the month and see exactly where your money is going and if you are overspending on what you have coming in or if it's just a cash flow issue at this point. Might help you with keeping things straight for next week and the week after if you know tht you will have the money for guides in three weeks time etc
best wishes
Gilly