Watches: the classic gender identifier.
Now, I know what you're thinking: "I'm a guy, so I'll get the 'his' watch!" or "I'm a girl, so it's a 'her' watch for me!" But c'mon! Don't be so close-minded! This isn't about choosing the watch for now. This is about what you want from your future.
Now, I'm know I'm just restating what everyone knows here, but as has been published in the pamphlets of the great Double Dr. (not just a doctor; a double doctor) Francis Clownman, our planet will be invaded within the next ten years by a species of aliens (the Trogors) who possess great power but cannot see above the average human wrist. Therefore, they will have no way of knowing if you human female or a human male except based on what kind of watch you're wearing.
If you've got on a Men's Throttle Black Ceramic Chronograph Watch with a Black textured dial and luminous silver tone hands and Arabic numerals, then you'll be sent back to the Trogors' home planet (Trogorptork) where you'll be forced to mine valuable torgnok from Photribik Mountain Range.
On the other hand, if you're wearing a Women's Karamica Collection Ceramic Watch with genuine black mother-of-pearl dial and slender silver-tone hands, you'll stay on Earth, but you'll be forced to do such Trogorian dances as the Zorbtrimik, the Twiznilip, the Zimprimp, and the Eiiiip, all of which were choreographed for the Trogor's twelve legged bodies.
Yes, neither life will be pleasant, but at least you'll be able to choose, and that's worth something, right? I mean, if they can only see as high as the wrist, then how else are they going to identify your gender? Although, I guess the wrist hangs around the waist, and there are those things at waist-level that are pretty indicative of gender...
Wait, you mean Double-Doctor Francis Clownman lied to me?