I think the nature of the question boils down to the circumstances that led to my decision. As I said before, the exact nature of why I decided not to go to the liquor store is not as important as the fact that those circumstances happened to be peculiar to that exact moment, when I was at the intersection midway between school and home. I recall there were other times when I was struck with that same dilemma at that same intersection only to make the opposite choice. I concluded that in each of these cases, my decision was a result of both external circumstances (my personal funds, how much liquor I already had at home, whether I had to work the next day), and internal circumstances (my mood, attitude, how much I wanted to get shitfaced). If, in each case, those circumstances led to one and only one decision, how could I have possibly chosen otherwise.
I did some looking around on the Internet and eventually came upon the Wikipedia page for determinism, the "philosophical position stating that for everything that happens there are conditions such that, given those conditions, nothing else could happen".
"Ah, yes," I thought as I skimmed over the article, "that all sounds perfectly reasonable." I rather enjoy the idea of free will, and I admit that confronting the possibility of it not actually existing was not nearly as horrifying as I anticipated. Except, wait a minute! Without free will, how can there be such a thing as personal responsibility!? I recalled that South Park episode where John Wayne Gacy, Jeffrey Dahmer, and Ted Bundy try to retrieve a birthday cake for Satan a la the Three Stooges. They run into some trouble when Gacy repeatedly goes out of his way to randomly stab passersby to death, saying in his defense, "I'm a victim of soy-cumstance!" If determinism is the law of the land, couldn't we all just be victims of circumstance, regardless of our transgressions against society?