You could buy 7-11 big gulp. After all that gigantic drink should last for the entire movie. Of course, it’ll get rather watery towards the end.
So then what about a nice Igloo cooler? That might not be a bad idea. You can find those in all sorts of sizes and shapes. All you have to do is buy ice and there you go.
Of course, some people don’t like the idea of lugging ice, draining the water, and throwing out soggy sandwiches. Plus there is the expense of constantly buying ice; however, it is cheaper than buying those big gulps.
Another option is to get a small refrigerator for your truck. TruckFridge is just one place you can look and see for yourself what is available and what the prices are, though you may need a power adapter or converter.
So as you can see, one great thing about our modern world is that you always have options!