Time and disposable income.
But you can also get into the more complicated aspects of nutrition, education, etc., they're all tied together.
I was just commenting the other day, as I was leaving for the office "late" one morning, on a conference call, and passed two neighbors who were doing the same exact thing, that it seems the more money people make, the more flexibility they tend to have in their schedules. Whereas minimum/low wage workers tend to be tied to a very strict schedule.