I will make a roast chicken, potatoes, veg and use the leftovers creatively over a few days - fajitas, stir fry, curries. I will make potato salad or chop up the leftover potatoes to fry with salmon, sea bass, cooked breakfast. Add roast veg to a large pasta bake etc.
I make soup and freeze in takeway containers.
Aubergine bolognaise is a favourite and portions freeze well - just cook fresh pasta.
Lots of salads with avocado, nuts, parma ham, halloumi, croutons from bread about to be chucked, leftover salmon, chicken, steak etc (not all together!) - lots of leftovers can go quite well in a salad, especially if you make a nice dressing - honey and mustard my favourite. There are probably quite good for losing weight as not much carbs.
Lot of this stuff is easy to take into work in microwavable containers- salads, soups, reheatable pasta and stiry fries. Sometimes I take leftover roast meat, potatoes, veg, chopped into bite size pieces and sprinked with gravy granules on top - i add a dash of water before microwaving and stir it a couple of times during heating - delicious! But probably quite fatty!
I know the food I make is quite high fat and often high sugar but I just have smaller portions.