The ploughman's lunch is supposedly from a bygone era, but any attempt to pin the exact time period down lands you in the 1960s. Although its origins are strongly in doubt, its ingredients are not.
First, you have the cheese. "Tradition" would dictate a nice hunk of Cheddar (English, of course) or Stilton. Personally, I'd love a bit of Stinking Bishop as an alternative. Just keep it robust and, above all, keep it English.
Next up, the pickle! No two ways about it, it's a Branston pickle all the way. (For those not in the know, Branston pickle is an English pickle relish.) There seems to be very little wiggle room here, though I did find a few references to using pickled onions in addition (not as a substitute, mind you).
Last, a hunk of bread! Fellow New Yorkers, I completely visualize Sullivan Street's Pan Pugliese in this role. Regardless of what you choose, keep it white, crusty and rustic!
Most recipes I found also included a salad. To me, this seems just a little at odds with the rest of the meal. A hunk of cheddar, a hearty loaf of bread, and… a bed of mesclun greens? It just doesn't sound right. I much prefer the idea of using that stomach space for a pint of beer to wash it all down with!
Though we might be a long way from an English pub, it just takes a bit of cheese and some imagination to get you there. Enjoy!