We’ve all heard “Best thing since sliced bread” and wondered if that was really the top food invention.
What do you think? Spam? Toaster Strudel, Rice-a-Roni? Or farther back, the pretzel?
Preserved food, easily. Whether dried, canned, salted, smoked, or freeze-dried, the ability to store food over long periods changed human life. It’s noteworthy that people came up with most of these before they had a theory for how they worked – Nicholas Appert was sealing and steaming food in champagne bottles long before Louis Pasteur was born.
I would say that genetically engineering food for higher yields ranks right up there. But that’s an “invention” that goes back some 10,000 years. You looking for something a little more modern?
Preserving food is a good one. I’d say that refrigeration is a huge part of that.
Another vote for refrigeration. Mac and cheese is a close second. 
I’ll third refrigeration. Without it we’d have no pizza rolls.
twinkies, they last decades.
canning is probably it, it can preserve more food types than other methods and for longer periods without further energy input.
drying and salting don’t require further energy but are limited in food types and have a medium time period.
cooling in the form of mechanical refrigeration requires energy and is short term.
freezing requires lots of energy and is medium period.
Aseptic packaging, aka “juice box.”
Good Lord, people, what are you thinking?
Obviously the greatest food invention is alcohol. Beer, wine, and distilled spirits.
I’m ashamed that I’m the first one to point this out.
About three weeks, tops, from what I’ve read (Big Secrets and Wikipedia).
30 seconds after opening. 
Fluoride, toothpaste, and tooth brushes.
They’ve given more to our enjoyment of food than any food I know.
Fire?
Well, I’d say cereal agriculture/storage is first, animal domestication second (mmm… bacon), and maybe third is domesticating spices. Salting/smoking meat and fish might sneak in there, too.
For something from the last few millennia, I’d probably agree with some combination of canning/refrigeration/freezing. If we have to be specific, how about the Can Opener?
Rocks.
It appears you’re looking for actual foodstuffs, rather than preservation techniques.
Meat. Eating your fellow fauna. Major, major breakthrough.
And if we move things forward into the age of extensively processed foods, ready-to-eat breakfast cereal is very nice.
If we’re talking about convenient, cheap, and filling (which is not to say nutritious or delicious), then I’m going with ramen noodles.
I don’t understand the hype about Ramen noodles. I can eat them occasionally, but not every day. They’re unhealthy, and there are other cheap foods like pasta. I’d rather eat spaghetti, or beans and rice, or peanut-butter-and-jelly sandwiches.
Chocolate!
Better yet, whoever thought to put chocolate and peanut butter together…