If you ever buy a soda, or a bottle of water, you will never practically get your money's worth.
Here is my reasoning: You buy and pay for the full contents of the drink. Say it was a dollar for a bottle of Coke. That's one dollar you bled for 20 Fl Oz, 1.25 pints, or 591 mL of soft drink. I prefer metric. That's 5.91 mL per cent. 591 mL per dollar. Got that? Good.
Now, suppose you drink that Coke. You drink it, and then you go to throw it away. Before you do, notice something at the bottom? Is that... some left over? Why yes, indeed, you did not drink it all! "Aha, Anna, I have caught your trick! But it's solved if I just drink that little bit left, right? Then I'd really have drunk a dollar of soda." Wrong. Try it. Take a look. Still some there! "Okay then, then I'll just drink a little more!" Here is where I must stop you, my friend, for you will never ever practically drink it all.
No matter how hard you try, you will never get the remaining soda. It will be so little that it'll cling to that bottom, mostly because at that point the level of attraction of the soda drop for the bottom of the bottle is greater than the force of gravity or the suction you can try to generate in the bottle. It's not coming down, in other words. In addition, there are likely microscopic molecules of your soft drink embedded in the bottle, where again the attraction between those molecules is greater than anything you can do.
However, this comes with a caveat. Notice I said practically impossible. There are ways you could get every drop. For example, you could fill the bottle with water to flush out the remaining soft drink, and you wouldn't have to worry about the water remaining. However, we want to get our money's worth, and filling said bottle with water will run you up a water bill. So it widens the gap between what you paid for and what you got, since with adding water you are adding to the cost of buying the soda in the first place.
You could also cut the bottle in half and lick the sides dry. The issue with this solution is that it's not practical to cut every bottle in half after you've mostly emptied it. Doing this in public may also elicit some stares and questions concerning your mental stability. It may also be illegal, especially if knives and scissors are banned/moderated where you are (where I work they have exactly one pair of scissors, under the auspices that they are a deadly weapon).
That leaves us with the question of how much do you get for your money? This is all important as it decides whether or not our concerns of being cheated out of our fair share are valid. By simple optical observation, we know the percentage of soda drunk is well above 85%. I would venture it can safely be assumed to be above 95%. So let us image a worst case scenario where you only drink 95% and the rest cannot be reached. You lose 5% of the soda you paid for. You lose a whole 29.55 mL (that sounds like and is a lot, but remember we high rolled it to assume the worst). That means you drank 561.45 mL of soda when you paid for 591 mL. Where you should have only paid 95 cents, you paid a whole dollar. You lose 5 cents of valuable soft drink!
Now, we have to ask ourselves: is 5 cents really worth worrying about? Would I notice or care if I lost at most 5 cents whenever I drank something I paid for? The logical answer is no, I would not care or worry. I would not even notice save for the fact that I am staring at an empty water bottle on my desk at work right now with drops of water still in it. It stays constant as well, in that if I paid for more bottles of soda, I would still only lose at most 2-3% of what I paid for, which might be 30-40 cents if I bought a truckload of soda (it would come out to 472800 mL at 591 mL/$1, or about 800 bottles). Since I never reasonably and in sound mind buy more than one bottle per day, over the course of a year I only lose $18.25 out of $365 dollars spent on theoretical soda.
Let's put a different twist on it: Let's say that the overcharge is a kind of tip. To whom does this tip go towards? The vendor is the logical answer. He paid for an entire bottle of soda, and he sold an entire bottle of soda so he... wait, he doesn't get anything out of this! He come out the same as if you drank the whole thing. The vendor does not notice anything at all. He can't add or subtract the amount of soda he receives and sells, therefore he does not gain anything from your loss. By extension, Coca-Cola Inc. does not get 'tipped' either, by the same logic: the vendor paid for their goods, and so whatever the company makes off of you isn't directly from you, but indirectly received from you via the vendor who uses your purchase to purchase more soda. Confused? Just keep in mind that no one is benefiting you not getting all the soda you paid for.
So we established that no one gains, you just lose out. We determined that you don't mind losing less than 5 cents on any given soda bottle you pay for, and since the vendor and producer don't come out ahead or behind they have no incentive to do anything about it. Everyone loses or doesn't care!
It's a non-problem in a pointless thought experiment while dilly-dallying at work.