In regards to food;
Aldi and Lidl will be your saviour for food shopping (especially fruit and veg) - although they don’t always have every product you need. I used to use them for fresh products once a week and spend about £10-15.
Bulk buying your rice, pasta, couscous (easy on the go food), tinned products, seasonings etc via click and collect (or delivery if you have the little extra) as they have a minimum of £40 but it’ll let you keep a running tab of the cost of your “cupboard essentials”. These should last you the whole term.
Also visit local pound shops (poundland, pound stretchers etc - they all have those sort of names) and bulk buy toiletries and cleaning products from here. This usually cost about £20 max per term.
Also remember, lots of places in London give you free food on your birthday (you can always lie about the date ) and there’s apps like olio which give free food from people who no longer need it.
And as everyone has said, plan your meals. Overnight oats for a week can cost you pennies, homemade lunches save loads and then meals which last 2 days - meaning you only have to cook 3 times a week!
Cutting out meat can also save you loads of cash - but that’s a personal / financial choice that some people make (I saved some much ). Hope this helps a bit.