A ploughman's lunch is a plate (or platter) of cheese, bread, sometimes pickles. Nothing fancy. I believe it is old English pub fare (never been to England, but had it at many English-, Irish-, or even Scottish- style pubs around the country and in an Australian place in Hong Kong). Meant to be hearty and fast. I will say this conditionally, just how I've had it, and I have often. I think usually accompanied by beer/ale of some sort.