If we're talking about big science&technology categories, I'd say:
Controlled fire (if you can consider it a "man-made creation") -> essential for food and a lot of manufacturing
Wheel -> essential for transportation, but also to make flour (millstones), and a lot of other stuff (e.g. turbines are, basically, specialized wheels)
Controlled electricity and electromagnetism -> artificial light, modern communications, not to mention medical advancements like X-rays
Insulin and pecillin -> millions of lives saved
the printing press -> knowledge becomes easier to spread
If we extend this to all kinds of human "inventions", including law, philosophy, religion, and so on, the list is even longer.
Controlled fire (if you can consider it a "man-made creation") -> essential for food and a lot of manufacturing
Wheel -> essential for transportation, but also to make flour (millstones), and a lot of other stuff (e.g. turbines are, basically, specialized wheels)
Controlled electricity and electromagnetism -> artificial light, modern communications, not to mention medical advancements like X-rays
Insulin and pecillin -> millions of lives saved
the printing press -> knowledge becomes easier to spread
If we extend this to all kinds of human "inventions", including law, philosophy, religion, and so on, the list is even longer.