Really like the ideas on here - especially the breakfast of oats, honey and banana. A good lunch, or tea is omelet buy 15 eggs at aldi for $1.25 - good value and will really fill you - buy frozen veggies - like peas to add to omelet or use any left over veg (if you have any) - buy parmesan cheese - again from aldi $2.30 - seems expensive but lasts and lasts and adds quite a bit of flavour to omelet without using a lot. Although you wouldn't do it all the time - you can add any left overs to the omelet like potatoes - dry fried, or onions, mushrooms, peppers, Two eggs, peas and a bit of cheese will give you a good shot of protein.
Def go to shops when they are reducing things - Tescos seem to reduce all day but big reductions come around 6:30 - 7pm, don't be afraid to hang around and wait. search 'frugal queen cornwall' - she does really good recipes for very frugal food.