Frozen mince is really cheap. You can use it for pasta bol. which can stretch for a couple of days or sloppy joes. A big frozen chicken is good for a couple meals. A couple bags of frozen veg are handy and will see you through the week. Buy pasta in the huge bag-it's cheaper that way. Only let yourself buy a couple of basic packs of biscuits (custard creams, ginger snaps) they will satisfy your sweet tooth but you won't get through them as quick as luxury biscuits. Instead of Ragu make your own sauce using tinned tomatoes. Buy a big block of cheddar, some eggs, milk. You've now got the ingredients for omelets and Mac and Cheese. All the super markets sell what they call cooking bacon which is great to jazz up pasta sauce, mac and cheese, omelets and is very cheap.
Have a look at the clearance stuff but be careful-a lot of that was overpriced to begin with and is high in calorie, low in content. Your better of making your own.
Also, if you're really on a budget look at the frozen meat-much cheaper.