I’ve done the occasional Tampa-to-St. Pete commute during peak times, and they can easily stretch to over an hour. For those trips, I’ve found a Starbucks “Venti” (Italian for “twenty,” and denoting 20 ounces of drink) or an American large-sized pop (varying from 16 – 30 ounces) to be plenty.
But there are people with longer commutes, stronger thirsts, and bigger bladders for whom the standard cup holder is not enough. Fortunately for these thirsty customers, there’s a whole industry of cup holder adapters, and within that industry, a specific kind of adapter: the half gallon milk crate adapter:

The ad copy for the version available at Walmart’s online store says it’s “Specifically designed to hold half-gallon square cartons, milk jugs, and large juice boxes that don’t fit in standard round cup holders”…
…and thanks to 3-D printing and the entrepreneurial spirit, there’s no shortage of Etsy vendors who can sell you one:

While I’ve never felt the urge to take a half gallon of ice tea, juice, or milk as my long-drive drink (mostly because the drink would get warm before I was halfway done), I’m pretty sure there’s a sea of customers out there who are looking for this kind of thing.
Besides, the adapter also doubles as container for keeping things organized in your car.