Good cheap lunch’s I can bring to work?

Cheap vs. Easy vs. Delicious--- best to have all 3 in one go so that you never have to buy a lunch.
I'm going to resound what everyone else has said --- leftovers are #1.
If you don't want leftovers, we often have yoghurt (buy a big tub & put into re-usable containers for every day of the week in the fridge) and add granola at time of eating.
Looking forward to reading more of other people's suggestions.

Let's assume you do not have access to a microwave or a refrigerator at work, but do at home, and what you really want are cheap, easy, and convenient lunches -- but also healthy.

*Peanut butter and (anything, in moderation) sandwich and an apple.
*Thermos of hot soup, especially if it's homemade and has vegetables in it. Five saltine crackers, or six Triscuits.
*Single-serving Greek yogurt and some baby carrots. Greek yogurt has high protein bang for the buck, and if you get the sugar-free kind it will probably be under 100 calories. Also, it's satiating. Add a pack of sandwich crackers (cheaper by the big pack at a grocery store). Please, if you're on a budget, buy groceries, not vending machine food.
*A cheese stick, half a package of the cheap lunchmeat (like Buddig's 2.5 ounce packs, but only if you're not worried about sodium), and two slices of bread. Maybe add a York peppermint patty for delight.
*A huge healthy tossed salad, but leave off the croutons and minimize cheese. If you must add dressing, then have a separate tiny container of it, and dip your bites individually. Single serving of crackers of your choice. By all means, add 2-4 ounces of a lean protein if you have it.
*At home, sauté some boneless chicken slices or other lean meat, season to your liking, and draw from it for sandwiches or salads through the week. I like pork tenderloin, too. Limit the fat and salt.
*Also, make soup with lot of vegetables at home.
*At home, microwave some sweet potatoes to grab and go. They are okay at room temperature, but better hot, and so good you really don't absolutely have to add butter or, well, anything. I eat them hot for breakfast, out of hand, as car food.
*Two boiled eggs, four ounces of something veggie, four ounces of something fruity. And a tiny piece of cake or something that makes you feel happy.
*Nature Valley protein bars make me happy. I watch for coupons and sales, and buy them in bulk at my warehouse store, where I can still, with a coupon, get them for about fifty cents each. I'm not saying go out and buy the ones that cost over a dollar each. A protein bar and some yogurt get me through.

Things like yogurt and salad will be okay in a lunch pack at room temperature for a few hours, really, but you could throw in an icepack if you are nervous.

**If it happens that you do have a refrigerator/freezer and microwave at work, buy some frozen vegetables. You can eat a whole 12-ounce bag of most broccoli mixes for about a hundred calories. I eat half a bag and that much microwaves perfectly in three minutes. Add protein if you have it, a side of yogurt if you don't have meat. You've had lunch for less than two dollars if you bought store brands.

I used to make Hummus, and a cucumber, cherry tomato and red onion salad w Greek style dressing and feta on a pita. Can add a little romaine if you have it, but not necessary. Keeps well in the fridge and much cheaper to make a big batch of your own hummus with chickpeas for the week. I don’t want the veggies to get soggy so I mostly chop/add them with the dressing while packing my lunch container for the day.

It’s also light enough that I don’t feel foggy from a heavy lunch. Feta can be expensive, but I’ve gotten it at Costco so it’s not so bad there. Maybe switch to a regular cheese stick
If you prefer.