Well, there's a problem: Macbeth compares life to more than four things.
He likens each day to a life in Act II scene 2, and refers to life as a "feast" in the same section.
In scene 3 he refers to the "wine" of life (blood).
When talking about Duncan after his death, he refers to life's "fitful fever," comparing life to an illness.
In one of his most famous speeches, Macbeth refers to life as a candle, a shadow, a player (actor), and "a tale /Told by an idiot."