This type of behavior is a coping mechanism when under high amounts of stress, ie controlling what they can rather than confronting the adversity of the unknown.
Well obviously supermarkets put the worst product in the easiest to reach place, so if you want the highest quality candy box or whatever's in there, you have to dig to the bottom.
What do you mean that doesn't make sense in this context?
The display looks better, and probably generates more sales in the "mixed up" state. The little hunt for discovery gets shoppers more emotionally invested. The mixed state looks fuller and more busy. Some staff member probably had to mix up all the candy initially.
It says "fake psychic. real detectives." with a fist bump underneath. It's a reference to a TV show called "Psych." I couldn't find the exact t-shirt he's wearing, and the only "official" listing I could find is in the NBC Store (I can provide a link if you want, but t-shirt links on social media always look a bit fishy, so I won't include one in this reply; you can also just go to the NBC Store and search for "fist bump" there).