What can I have for a really cheap lunch?

Bring a sandwich from home. It only takes a few minutes to put some kind of a spread on some bread and bring it to work ie peanut er, jam etc. If you have a bit more time to spare you could make a ham and cheese or tomato and cheese sandwich or some thing a little bit fancy is smoked salmon and cream cheese. Just make sure you keep it cold ie with an ice pack if your using any kind of meat. You could also make your sandwiches in advance and put them in the freezer as you come to work ie make them on the weekend then freeze.