Look at what the Mayans did without the wheel.

auto tint welding goggles

Sorry for being a smart ass but i gotta say the wheel. So transportation

i cant believe no one here picked lighting devices. if theres none of that, then we would lose night, which is a huge portion of our lives

If there was no heating we'd all still be in Africa

If you're talking about fire, I don't know if that really counts as an invention.

Simple- Currency/Money.

In the scientific community, the number one thing holding us back is funding. Money gets things done. Any graduate or research fellow will tell you that.

Then that could be seen as the worst invention....

I'll have to say Electricity, because none of the above work without it.

Coolent and heating Devices (freezers,fridges,Heaters,Air conditioners)

you need this the most so your food doesnt go bad
unless you wanna use salt