Ships are much more efficient than cars. Having said that, this wouldn’t have a huge range, nor is it terribly big by container ship standards.

My vote is definitely for fire. Learning to first contain and sustain, then how to create fire. Everything else follows on from that.

Cooking food probably started us down a path to become as intelligent as we are today.

And the light allowed us to have free time at night to try new ideas.

And the warmth allowed us to spread out of Africa.