I used to do it as an undergrad (2009-2012), now I still shop as economically as possible, but I have a larger income. Shopped at Aldi or Lidl, or Tesco/ Sainsbury's basics range; if you compare the ingredients and their ratios for supermarket range stuff and more expensive branded stuff, a lot of the time what your actually paying more for is the nicer packaging and brand. It's often also cheaper to buy loose fruit and veg - and that way you can get as much or little as you need so you're not overbuying, and you don't waste food. If you're saavy - especially in the reduced section, you can get decent but going-out-of-date bread, meat, etc. very cheaply, and then put them in the freezer the same day, and defrost and use as required.
Cook from scratch, and in bulk (tupperware and the freezer are your friends). Cooking from scratch is healthier too.