Personally my favourite, even above and beyond things, for entertainment value was getting letters from school kids.
Not high school kids who may have their own a-hole agendas, but young kids who draw hilarious pictures and ask questions like "Do you use jetpacks" or "Can you please kill ________ for me, he stole my bike".
One of my friends received a crayon-drawn picture of a stick figure Canadian soldier shooting a ton of people in the head, and all of the bodies had the X over the eyes, etc, which seems morbid now, but I can just imagine the teacher looking in front of the class saying "now we're going to draw nice pictures that show support for our soldiers..."