This is a harder question to answer than it seems

I would say heart, but acearo people exist

I have seen people on the internet say that they or other people have no brain and people cant lie on the internet so that isnt an option

I heard they faked the moon landing; to achieve such realism you would need to film in an environment with no oxygen and since you cant expect everyone to wear a space suit lungs are eliminated too

The stomach seems important, but i realised that if i stop thinking about food, the hunger goes away

Considering that some people survived without the left kidney and others without the right kidney, neither are important

This list is not exhaustive, but it seems like no vital organ is one we cannot live without