The siege has always been an effective military tactic, because people need food to survive. Being the master tactician that he is, Lord Vader always strives to foster a spirit of brotherhood among grocery store employees due to the their access to vast supplies of food. By having friends at grocery store chains, Vader is thus protected from someone trying to besiege him and also has the possibility of laying siege to his enemies, should it come to that.
Lord Vader also knows that he's getting old, and that soon he will have to pass on his throne to a worthy successor. Being the Christian that he is, Vader knows the parable that says that "he who is faithful over few things shall be made ruler over many things," and in keeping with this principle, one of the determining factors for who his successor will be is their love displayed towards grocery store cashiers. This is why for tomorrow, Vader wants to see everyone give a grocery store clerk a high five, and not only that, but also capture the moment on film, without them being aware that they're on camera. There is no room in the empire for scripted love. Vader wants to see the genuine article, and wants the videos posted on this, his illustrious site. It might help to bring a friend, who can record secretly while you give high fives openly.
Video of a clerk being high fived: 5 points
Video of a clerk getting double high fived: 6 points.
Video of you hugging a clerk: 10 points