It doesn't matter what it is as long as it contains alcohol. Nick and Mary's sexual interlude occurs after dining out and consuming a large amount of wine. While intoxicated, the two both drive their cars to Mary's house. Later, Mary drinks and drives again. It is implied more than once that Mary is an alcoholic.
Cigarettes also make an appearance.
There's one major negative element of Pushing Tin that I've saved for this summary statement. Russell is known for his bravado and foolhardy stunts. Early in the film, videotape is shown of him standing on a runway directly under a giant 747 jet as it lands. Later, when Nick's life has unraveled, he comes to Russell for advice on how to straighten it back out. Russell takes him to a Southwestern airport, and the two stand on the pavement, waiting for a jumbo jet to descend.