A blonde, a brunette, and a ginger drive into the desert.

Their car breaks down and the three decide to try and hike out of the desert together. However, they quickly get into an argument over who was more prepared for the situation. "I was WAY more prepared than you!" The ginger yells. "I have all I need to stay rested and ready to go!" Grabbing her backpack, she storms off into the distance.
"Oh yeah?" Yells the brunette, "I'm TONS more prepared than YOU! You can be as rested as you want, but what happens when you get weak and slow? I have all I need to stay strong and fast!" The brunette grabs her backpack, and runs off into the distance.
The blonde, not wanting to feel left out, yells to the other two, "OH YEAH??? Well, you can be as rested and as strong as you want, but what happens when you get too hot? What happens when you need to cool down, huh??? I have ALL I NEED to stay cool and refreshed!!!!" The blonde grabs her bag and trudges off into the distance.
After a few days, their families begin to get worried. They call the police, and a search party is sent to find the lost travelers. The first girl they find is the ginger, just barely alive in her tent. The rescuers asked what happened, and the girl replied, "We got into an argument over who was more prepared, and I thought I was because I had a tent to rest in. But soon I realized that, no matter how rested I was, I had nothing to fill my belly. The brunette had something to ease her hunger, so I guess she was more prepared than me..."
The rescuers kept looking, and after a few more hours they discovered the brunette lying in the sand, barely clinging to life. The rescuers asked her what happened, and she replied, "we got into an argument over who was more prepared, and I thought I was because I had food to keep me strong. But I quickly realized that, with every step I took I just got hotter and hotter. The blonde had something to keep her cool and refreshed, so I guess she was more prepared than either of us..."
The rescuers returned to their search for the last girl, and it took them the rest of the day. They were about to call it quits until they saw a body lying in the sand, its bones picked clean by vultures. "It must be the blonde," one of the rescuers said.
"But how can you possibly tell?" Another rescuer asked. "There's no skin! There's no clothes! There's not even any hair! It could just as well be anyone!"
"But it is not," the first rescuer said confidently. "I am certain that this one is the blonde."
"How on Earth can you tell?!" The second rescuer shouted.
"That," the first rescuer stated, pointing. The second rescuer let out a thoughtful grunt as he noticed the car door pressed against her side, its window rolled down.