I read some of the past winners to get an idea of what I should aim for. I couldn't determine an exact formula, but the winning entries seemed to have the most story condensed into them. So I wrote with that in mind.
Of course, I produced more than three. Here's what I wrote (some of you will recognize the first, as modified from one of my Twitter Fiction tweets):
#7. "Honey, I've decided to poison the neighbors, so it's best you don't eat any of those freshly-baked cookies in the kitch... oh, crap."
#6. She wanted to watch the sun set. He wanted to have sex. What's the best way to face the world's end? Actually, there was time for both.
#5. His watch was broken. What was it the March Hare said? Lee clutched his stomach, bleeding. Ah. It was the best butter. Lee smiled, dying.
#4. For best results, it said, take on an empty stomach. Which I did. And wished unicorns were real. I regret I didn't wait another hour...
These are the three I submitted:
#3. "So, was that the best you ever had?" "Well..." "Come on, you screamed!" "Um, actually, that was when you stepped on one of my tentacles."
#2. For best results, it said, think of others. Oh, I did! I wished angels were real. Their flaming swords, meting out revenge. So beautiful!
#1. It's for the best, we said. We'll go, and let the Earth recover. Now, the winds howl across a global desert. Can planets die of loneliness?