I love these classic bubblegum trading cards featuring characters and scenes from the Star Wars movies. More here. According to this 1971 article, collecting bubblegum trading cards is a popular pasttime not only for kids but adults as well. Some of these cards can even fetch a cool thousand dollars or so. Most collectors get their cards from Topps chewing-gum packages or Kellogg's cereal and Milk Duds candy boxes.
(Thanks Lord Kimbo)