One of my favourite packed lunches is moroccan cous cous with roast veg.
I keep old butter tubs & put my cous cous in it, buy some disposable cutlery from poundland, and once your finished, throw away the tub & cutlery, saves carrying dirty dishes around & washing up when you get home!
Other ideas apart from the usual sandwiches, flask of soup etc. are - pasta salad, john west light lunches are good with some salad in a tub, prawn cocktail, crackers & cheese, & coronation chicken. If I think if anything else, I'll post them later