At the risk of sounding awfully superior, I'll say I used to eat really healthy stuff back when a student and skint. Possibly because I was REALLY skint and two pound of veg from the packing up market stall cost a bit less than a takeaway pizza or chippy.
A whole head of lightly boiled cauliflower with a couple of fried eggs tastes much better than it sounds. Heavily curried carrots with rice will help you ignore the absence of meat. And if you've never had a fried onion sandwich - you haven't lived.
This is one of the dishes that take me back. Mushrooms are an excellent source of protein and fibre. Season them generously and fry them with garlic - so tasty just with a chunk of bread. This is of course a suggestion for a side - my student days are far behind me and I do enjoy a bit of fillet steak with them every now and then, thank you very much.