To partake in the use of marijuana.
From Hank Williams Jr's song "Family Tradition":
Hank: "So don't ask me, Hank, why do you drink?"
Crowd: "To get drunk!"
Hank: "Hank, why do you roll smoke?"
Crowd: "To get high!"
Hank: "Why must you live out the songs that you wrote?"
Crowd: "To get laid!"