There are several products out there designed for salad lunches. They’ve got separate dressing containers (so everything stays crispy) and built-in cool packs for those without access to a fridge. Mine also has a built-in fork. I am not packing lunches at the moment, but when I was, my most typical lunch involved whatever salad greens I had in the house, some bulgur, a ‘sharp’ (scallions, chopped red onion or shallot, or perhaps diced radish) and then other stuff I had around. That might be leftover meat/chicken/salmon, beans, chopped salad-type veggies, nuts, dried fruit, leftover simply cooked vegetables, or whatever else looked good. Toss some olive oil, vinegar of choice, honey if you like, salt, and pepper into the dressing container, and you’re good to go!
If I was rushing, I’d take some humus in a little tupperware, grab a yogurt, and buy a whole-wheat roll from the bakery on my way to the car (the bakery’s around the corner, and the car was wherever I’d found parking). Add a good-sized serving of fresh fruit, and you have a pretty well-balanced meal.