Since rmc28 and dorianegray have already given you most of the food suggestions I'd have thought of, the only thing to add is that if you make a bunch of different things in bulk (aim to cook a major bulk item each weekend for a few weeks, for instance) then you always have something different to take in to work, or to eat at home when you don't have the energy to cook that night. Soups are really good, but my mainstays are shepherds pie (I can give you my totally knockout recipe if you don't have one), spag bol, and risotto. With shepherds pie, you can't really freeze the potato bit, but you can make the mince in advance. Then I cook enough for four, and Adrian and I eat half that night and there are two portions left over for the rest of the week. Cooking for at least double seems to be a generally useful trick.