Home Bargains sell Koka noodles 3 for £1.20, this is better value for money than pot noodles and they are really nice. I like curry flavour, personally, and have had them in the past when I was struggling for food.
They also have Nakd peanut bars that are very filling and also nutritious, 4 for £2.
Bananas are very filling and nutritious, yes strictly speaking perishable but can be kept in cupboard, same goes for apples. Try and keep bananas away from other perishables though as they emit something that makes other food go off.
Home Bargains also has those individual fruit packs mentioned above, fruit in little plastic pots.
Another great call for calories are peanuts, you get an enormous amount of calories for not much money. Home Bargains also has little 40g snack packs of these for about 35p and they will fill you up and give nutrition for not much money.
Peanut butter
Canned sweetcorn is also cheap in a 3 pack from Home Bargains
Crumpets are very cheap and filling
HB also has the individually packaged chocolate croissants and brioches mentioned above
Lidl do a pack of 28 own brand "Siempre" normal winged sanitary pads which I find the best value around.