Al probably doesn't feel too bad about a late night food rummage; he was V.P. to a man whose second hobby was jogging to McD's (You can probably guess what the other hobby was. )
I haven't seen "An Inconvenient Truth" but I can imagine that it does the usual job of demonizing large corporations, thus unintentionally allowing the average citizen to shirk his or her responsibility for change. If you've ever watched "Super Size Me" or "Roger and Me," you know what I mean. The filmmaker portrays corporations (Fast food and Car Makers, respectively) as so evil and so powerful, that instead of feeling outrage, people come out saying there's no hope to do anything about it. As a result, instead of making small changes in their lifestyle to make any difference, they are basically unaffected.
Maybe Al is just like others seeing his film... he saw it, felt passionately that the companies were wrong and went in search of a snack knowing that what he did was nothing compared to the 'evils' perpetrated by Big Business.