1.Prepositional phraseAbstaining from drinking any alcoholic drink, usually in the sense of having given it up (as opposed to never having partaken); teetotal.
2.Prepositional phraseMaintaining a program of self-improvement or abstinence from some other undesirable habit.
"He’s been on the smoking cessation wagon for two weeks now."
3.Prepositional phraseUsed other than figuratively or idiomatically: see on, the, wagon.