Nondescript Beverage is a beverage that Tim drinks occasionally.
Nondescript Beverage originally appeared in Episode 8 of Super Mario Maker, A Shift In Management, at 0:48. The running joke is that Tim keeps drinking it, and despite his terrible camerawork (He once commented that his fingers had "never been on so much film"), the drink never goes on frame.
Tim confirmed that it was, in fact, a beverage, but no further details were given until Episode 10 of Shovel Knight, The Tom Hanks Rant, wherein JT accidentally mentioned it was a root beer. It was then joked that the brand remained unknown, and game-play continued. JT created the hashtag #StillNotAnAd for videos in which the beverage is mentioned.