Buy a wide mouth soup thermos …. and make up some soup or chilli and bring to work.
I put up a veggie container with hummus or other dressing … with my particular favorites cucumber slices, grape tomatoes, etc. could add some cold chicken or something like that as well to your veggie assortment.
canned sockeye salmon salad …. full fat mayo, lots of finely chopped celery maybe a squeeze of lemon or whatever you like in salmon and tuna salads (i like the solid tuna canned in water) … and if the red sockeye salmon is on sale i buy up a bunch. Heck you can make chicken salad or crab salad.
Bring some left over supper from the night before. I used to love cold pork chops!