Baler twine in particular received many votes, with contributors vying amongst themselves to record its multitude of secondary uses on the farm: everything from calving ropes, to an emergency repair on a water main, to replacement bucket handles. No farmer it seems leaves home without a few strands in his pocket, just in case they might come in handy to mend a bit of fencing or tie up a gate. 
It all goes back to the introduction of the reaper binder which by the 1890s was tying its sheaves with string, rather than the wire that was tried first. Binders were later replaced by combines but hay and straw balers continue to use large quantities of twine. Originally, the string or twine was made from fibres of the sisal plant but since the 1970s, polypropylene - a very strong and virtually everlasting man-made fibre - has taken over and become a ubiquitous part of the countryside.
Wellington boots were amongst other items mentioned. It's difficult to imagine life without them. I don't know when rubber boots became commonplace on the farm. We'll have to start logging their appearance in the photographic archive. This is an image from 1947:
