Of course you also have the option of throwing an ice chest in your car, stocked with whatever sizes of soda you prefer. You could save tons of money, and entirely eliminate waste, by buying 3 litre bottles of generic sodas for $1, and using whatever size cup/bottle you prefer.
That's not a solution. Go back and re-read what I said about the 20 oz. going flat before I could finish it.
Generally, you didn't comprehend much of what I wrote. Coca Cola is a *treat* for me now, not a staple like once was.
That said, it's interesting that through your mist of incomprehension you actually came close to mentioning some things I do now.
If I'm on something other than a grocery run, like a day trip to the beach or something, I do pack a cooler. I have a couple of Glacier (TM) water bottles that are reusable. Theae are available at Whole Foods near here. You pay $6.99 for 750ml of water, which sounds crazy until you factor in the fact that you're getting a reusable stainless bottle for much less than what empty stainless is often sold for. I'm not affiliated with either company.
For the fizzy craving, travel sized Welch's grape juice + Perrier. Once again, not affiliated with either company. This makes a fantastic grape soda, and you know that everything in it is good. Once again though, this is only for an all-day trip. Yes, Perrier makes a difference--it's got a "bite" that I only used to find in Calistoga sparkling water, which is no longer available here.
Maybe now you get the idea that I'm not going to be satisfied lugging over-sized bottles of ever-flattening generic HFCS infused soda around in my car.
The problem of right-sized Coca Cola not being widely available remains. Also noted, It's definitely a "first world problem" we're whining about here.