The next big thing to consider is where you shop. Of course, the Tescos Express around the corner from where you live is very convenient, but is it the most cost-effective? The extra metro trip to get to Lidl, for example, might seem like a pain, but the amount of money you save is well worth it. The Lidl Plus app also offers some great reductions, like the odd free pastry, the more points you save up.
Grainger Market is another cheap option for fruit and veg; and not only is it cheaper, but the products are generally better quality than supermarket veg as well. Shopping here is also a way to support local businesses and give back to the community rather than only shopping at big chains.
One last tip for saving on food is how you organise your meals. Cooking for one can be a challenge in a world that sells food in family-size quantities. To combat this, and to avoid food waste, try to plan meals that will use some of the same ingredients - or make big batches and freeze the left-overs. For example, if you are making fajitas one night, any left-over veg (onions, peppers etc) would go great in a curry as well. Think ahead, and try to coordinate your meals with the ingredients already in your fridge.
Hopefully by making these small changes you will be able to save up that small change which can make all the difference when living on a student budget.