Well, maybe not the winner. I actually still don't know which take-away container is the most common. However, the bag is indeed proving very popular for cold drinks. I see it all over the place, and have now been given a few myself.
Sugar cane juice with lemon:
Note the straw sticking out of the bag. The vendor put the half lemon in the bag, tightened the bag and squeezed it (oh the convenience!) then added ice, (freshly pressed) sugar cane juice and a straw. (I should add that this was possibly the best sugar cane juice with lemon that I've had here.)
Also used for iced milk tea:
Someone in front of us in the milk-tea line bought tea for four -- and it is definitely easier to carry four of these one handed than four cups (maybe even when those four cups are in a carrier). The coldness of the ice also circulates better in the bag than in a cup.
And here's how you drink out of the bag:
Although you can't really see it in this photo (yes, the camera does take videos ... if its user switches from camera to video mode), James is in motion -- a key element to the bag take-away format because the fact of the matter is, you're not going to be able to set the bag down on your desk (oh the inconvenience!).
You could, of course, pour your beverage into another vessel (like we did the Indian food). James suggested that one could instead hang the bag from a coat rack or doorknob in your office. Now if I could just find a 10-foot straw ...