Car problems

Three men are in the middle of a desert when their car breaks down.

For their hike to town, they each decide to take one thing with them.

One man takes a jug of water.

The second man takes a sandwich.

The last man takes one of the car doors.  

The first man says to the last man: "I'm bringing the water because if I get thirsty, I can take a drink. And it makes sense to bring a sandwich in case we get hungry, but why bring a car door?"

The last man replies

Spoiler:

"If I get hot, I can just roll down the window".