“To bag school: to play hooky. Chiefly Pennsylvania, New Jersey.”
When I was going to school in Western Massachusetts in the early 1970s, “bagging” something was synonymous with avoiding, blowing off, gaffing off, or whatever alternative you like. It was not restricted to school itself: “Wanna go out?” “Nah, let’s just bag it.” (Meaning “Let’s stay in.”) Or “I’m too tired for a 9pm movie that’s gonna last till eleven, let’s bag that.” “Did you do the reading for today?” “Nah, I’m baggin’ it.”
So there may be more to this than you realize.