On the go, travelling around the country, my emergency lunch is a pack of ham/salami (check sugar contents) and a pack of sliced cheese. Roll a meat and cheese slice together and eat.
With lots of time available, I might make a vegetable soup (spinach, mushroom, tomato for example) or crustless quiche or chicken liver pate.
You can eat anything for lunch, doesn't have to be sandwiches. Remains of last night's dinner is always an easy one, or a chuck of cheese.
Sally