The story I heard was that the original Toll House was an inn or a restaurant. The woman who cooked there was already known for her butter cookies. One day she wanted to try making a chocolate version, but didn't have any cocoa powder. Instead she used chopped up chocolate, figuring the chocolate would melt during cooking.
The rest is history.
The chocolate company came up with the "chip" idea to make it easier for home chefs to make their own cookies.
As for the most important invention in history...I'd have to say the plow.
The plow made it possible for one man and an ox to do in a day what it would take a whole crew a week. The increase in crops meant you had a surplus of food, which then allowed people to do something other than worry about the night's meal - like developing the basis of what we now call culture, religion and science.