Sorry to hear you're going to be financially restrained for a while...
This is how I manage not to spend too much money:
1. First of all, pick a shopping day and time when you're not in a rush to get round the shops and have time to compare prices etc. Preferably a day off when there's time to do some pricing up before you go too.
2. Get 3 pieces of paper - one for what you've already got, one for what meals you're having that week, and one for the shopping list.
3. Go through your fridge and get rid of anything that's out of date. Then go through your freezer, fridge and cupboards and work out if you can make meals out of what's there already. Write these meals onto your meal planner, but if no meals can be made, that's fine. Assuming you're not vegetarian and do a mix of red and green or EE days, write down any meat, fish, quorn (ie. meal basics) that you've already got and how much of each on your second bit of paper.
3. On your shopping list, write down what you need to buy to make your meal basics into meals - herbs, veg, pasta, rice, etc.
4. Assuming that you haven't got all the food for 7 dinners and any lunches you need, now decide what you want to eat for other days and nights. I start by going online to websites for Sainsbury's, Tesco, etc and see what's on offer. If chicken's at a good price, for example, then that's a good choice for that week. I'd recommend if you're cooking most nights then make twice what you need as long as you can freeze it afterwards. Then you'll spend the same time cooking but already have some of the meals for next week done. This avoids having to have leftovers for lunch or dinner the next day!
5. Add the rest of your food onto shopping list that you need to make all the meals for that week. If you want, you can put it into mysupermarket.com to see which supermarket's cheapest, but I find if I'm making good savings on expensive things like meat, a couple of pence here or there on other things doesn't make too much of a difference.
6. Go shopping! Stick to the list, or agree that you'll only spend a certain amount on non-list things like treats - e.g. £5 on things you see when you're going up and down the aisles.
Other tips: Beware Lidl and Aldi! Some things are cheaper, but a lot of the stuff they have is more expensive that the supermarkets (people spend money because they think everything's cheaper than the big supermarkets, but it's just not true)! If you have time, go to Lidl or Aldi first but note down on your shopping list how much Tesco (or wherever you shop - check online) charge for the same thing - only buy what is cheaper and I think you'll be surprised at some of the 'budget' prices!
Buy reduced food if it can be frozen and you'll actually eat it! Meat, fish and bread are all fine if frozen on the day of purchase. Reduced potatoes can be boiled, mashed and frozen fine for quick defrosting later. Figure out what time your supermarket reduces food, and try and pop by then to see if there's something worth buying - but remember, only buy it if you can use it immediately or it can be frozen, and you'll eat it!
Hope that helps and that it wasn't a too terrifying insight into my household shopping ways!
Every weekend I sit down and plan what meals I'm having for the week and write a shopping list before I go. Make sure I have a hearty breakfast before I head out to stop me from feeling hungry whilst I'm there and most importantly completely avoid the tempting chocolate aisle 
