Leftovers from the previous night are great for lunch. I often take moussaka or chicken with olives in to work.
Otherwise either the smoked salmon & chicken salad or I prepare something the night before like chicken breasts (you can buy these ready cooked but remove the skin if it was roasted with sugar) with steamed green beans tossed in olive oil, lemon & black pepper. I then eat that cold.

It is cheaper, and quicker, to take your own lunch than queue up to pay for sandwiches & crisps that are going to make you fat & have you craving more carbohydrates by mid-afternoon.

The low carb gourmet book I read had a delicious recipe for pizza quiche which would be great for lunch. It was made from eggs, tomatoes & sausages I think. I will find out.