Left overs are popular in my lunch box.
And soups/stews- prawns and noodles in miso broth, chicken soup, chickpea and lentil soup, butter bean soup, Mexican bean soup,, spring veg etc.
I also have salads, Beansprouts, chilies, coriander, shredded Chinese greens and prawns or rocket, chicory, radish and goats cheese, standard ham or chicken salad, leftover roast pulled pork salad, cous cous makes a regular appearance, and bulgar wheat.
Jacket potatoes, you can cook two or three on a Sunday to take in to work- they keep for ages in the fridge and just need reheating- make your toppings on the day- chilli, egg mayo, coronation chicken, ham and cheese, beans etc. if I were more organised I would put single portions of curry, Bolognese, chilli etc. to freeze to go with my jackets, but I rarely manage it.
I often end up with just stock, chilli and noodles- fine noodles cook in a minute in boiling water and can be dropped straight into your broth with some coriander and chilli flakes, but that's hardly inspirational.