Not sure if you're allowed to use a kettle in your room, but gyp rooms have them. As Visesh said, bring a duvet. I didn't personally have any problems with the pillows, but you could bring those if you wanted. No need for pillow case or sheets, but some people find the sheets annoying as they are the kind you need to tuck under the bed, rather than stretch around the corners.
I don't spent much on food, but I never eat in hall more than once a day. Breakfast can work out pricey (if you're going to have cereal in hall you might as well buy a big box from Sainsburys...I realised this after the first day), but brunch on Saturday and Sundays is worth it. Lunch and dinner are very similar to one another, and the costs vary. Generally, you'll ask for one of the options e.g. chilli which would be about Β£1.80 but then no-one really has that by itself, so you'd get rice/veg to go with it. So typically, you'd spent anywhere between Β£2 and Β£3 on a meal in all, not including dessert if you want it. I'd definitely recommend eating in hall in the first term though as it's sociable and everyone seems to do it. So basically, I'd say buy your own breakfast, and then go to hall for lunch and dinner in your first term...then after that see how you feel.
Edit: And as for mini fridges, most rooms have them but TCR don't. If you're in TCR you might want to bring your own.