root vegetables are cheap now so you could buy a bunch and just roast them in the oven for a while. i tend to cut them to smallish pieces and roast them for way too long and then eat with some yoghurt based sauce. do note that this is really boring to reheat. on root vegetables you can also make soup with the roasted pieces, add some broth and mix it together with spices or w/e you got and the roasted vegetables. also works well with butternut squash (probably pumpkin too but i haven't tried).
cabbage is also fairly cheap so you could fry it with some chili, garlic, and meat. i usually use pork but i suppose any meat would work. brussel sprouts are amazing in general and somewhat cheap now so could do the same thing with that.
maybe you could make some sort of wrap if you want to bring stuff with you? like hummus or refried beans with assorted veggies and sauce in some flatbread.
if you have a microwave or oven available you can always make tons of stew and reheat with rice or pasta, super easy and fairly tasty. i sometimes do a stew with chickpeas, coconut milk, and curry paste + whatever stuff i have at home and it always turns out ok.