So simple, I'm sure someone else has already come up with it, maybe even owns a patent on it, but, none-the-less, here it is from my perspective.  I'm sure you've all run into this at some point.  You're standing in front of a soda/juice/bottled-water machine, you put your money in, make your selection, and then become exasperated when you learn the Dr. Pepper is sold out.  You couldn't possibly know that until you make your selection, and your money's already in the machine, so you make a secondary selection only to learn that all the Root Beer is gone, too.  Well, shit, now you're really hacked off because the only choice left is that horse-piss, Mountain Dew, or nasty rat poison, Pepsi.  (Coca Cola's not so bad, but it's still #3 on the list).  Aggravated beyond you're normal levels, you try to get your money back only to learn that the coin return button has been broken since, oh, I don't know, the DAWN OF FUCKING TIME.  Grudgingly, you push the button for Pepsi because, god knows, that's never sold out, take your rat-poison, and wander away imagining all the horrific things you'd like to do to the company that just cheated you out of $0.65.

But this could have all been avoided, dear reader, if that vending machine had one simple feature, something I'm sure would be simple to install and easy to maintain:  A running count of how much of each soda is present in the machine.  Simple.  When the machine is restocked, the correct number is entered into a small computer which controls a small, digital counter on each of the machine's buttons, displaying for all to see which sodas are in stock, which are dwindling, and which are sold out.

WHY DON'T THESE COUNTERS EXIST?!  DOES SOMEONE ACTUALLY OWN A PATENT ON THIS?!  DID THE SODA COMPANIES PAY THEM TO SIT ON IT?!  WHY WOULD THEY DO THAT?!  HOW AM I THE ONLY PERSON COMPLAINING ABOUT THIS?!  WHY AM I WEARING A STAR FLEET UNIFORM?!  AAAAAAAAAAAAAAAAAHHH!!!

- CAPT Blood