not a fulltime student (yet) but i do live alone on a limited budget.
COOK IN BULK. Cannot stress that enough. Buying food for one is a pain (and expensive). Mince meals (drain the fat of cheap cuts) and fill it out with onions, carrots and gravy. Plus spuds are cheap and filling. Make a large meal that will do you for several evenings and divide it up into takeaway plastic boxes (get em in the pound shop if you cant afford a takeaway)
Baked beans are the most versatile thing ever, fill out spag bols, stews, sheppards pie, risotto etc. Just please avoid the Lidl own brand they are utterly vile
One of my go to's is scotch pankcakes - flour, egg, milk, baking powder, caster sugar (leave out if you want savoury). Top with anything and bam quick meal right there.
Invest in a rice cooker - bout £15 from Lidl and its brilliant for rice, veg, fish, chicken.
Make lunch to bring with you to college/uni
Living on a budget isnt that hard with a bit of planning