If you want to stick to veggies only, then the only option you have left is prepare your food day before, put it into little topper-wear dishes and take with you. Besides salad, you can cook your veggies and take them. If you saute veggies in olive oil with some spices you should be able to eat it hot or cold. If you have access to microwave to heat it up even better, I learned to eat my food cold.
Try making chips out of veggies (there are kale chips somewhere in the recipe section, but you can make it out of almost any other approved vegetable). That would be a good snack to keep you busy at work.
Once you introduce eggs, besides obvious hard-boiled eggs, you can also make vegetable/egg omlettes such as zucchini or spinach and those travel very well, even taste very decently cold IMO (FYI spinach should not be reheated after initial cooking).
Once you introduce oat bran, you can soak it over night, cook it in microwave few minutes and pack in topper-wear dish to take with you. I make it out of three to four tablespoons of oat bran, eat half for breakfast and half during the day as a snack. This is a great snack for me to keep me full. I didn’t make it today and I have hard time getting through my day, especially since I had just a salad for lunch. I have one more hard-boiled egg and a slice of my oat bran/buckwheat bread left so hopefully I make it til the end of the work day 🙂