If you can buy a few bruised vegetables for a few p you will be able to make your own soup easily, and it will make more than a few tins.
Here's what you need for a basic soup: 1 onion, 1 or 2 carrots, one stick of celery, any other odd vegetables or leftovers that are around. Add a couple of litres of water and simmer for about half an hour. If you have had any take away chicken, don't throw the carcase or bones away, put them in your soup too.
Or, over the next week or so, buy a packet of lentils (very cheap), and some dried peas. With the peas, you soak them in water overnight, then rinse really well the next day. Put in a pan with an onion, or whatever else you've got. If you can, get hold of some bacon bones, bacon pieces, and simmer for about an hour. Makes beautiful soup. You can put some into containers for another day. Put them in the freezer, using old milk cartons, or plastic containers.
At some point, invest in a packet of chicken stock cubes. Add one or two of these to the soup you are making. Stock cubes don't cost much at all, and they are usually found near the spices, flavourings, gravy mixes at the supermarket.
Soups are much more nutritious than cereals and toast. The pot noodles aren't very nutritious either, but they too can be put into the soup.
Here's another cheapie. Buy a can of borlotti or other sort of beans (not the ones in tomato sauce). Buy a tiny can of tuna. Buy one of those packets of instant rice, that you're meant to microwave. Open up the rice, and take out 1/3 of a cup of the rice. Add 1/3 cup of the beans, and microwave it for one minute (cover it up first or it will go everywhere). Then, stir in the tuna. You can use the whole can of tuna, or just half, and it will make a very very nutritious meal that won't put weight on you. You still have 2/3 of the rice and a lot of beans left, so you can do this several times from a packet.
It's all about gradually putting a few nutritious staples into your cupboard. Dried peas, lentils, dried beans, stock cubes, rice (much better than noodles for your figure), split peas.
Take a walk around your neighbourhood and check out the fruit and veggie shops, look for mark-downs, slightly less fresh looking stuff. You could also try growing some tomatoes and lettuce in pots. I do it, and it works out well. I've always got the basis of a salad there. Bit of cheese and I've got a tomato cheese and lettuce sandwich. Save the seeds if you buy any bruised tomatos, try growing them.