Perfect for notes to campers throughout the year
I work at a summer camp and pre-address several packages of these every summer before my campers leave. Then, throughout the year I drop notes to each camper sporadically. They always know to look out for a random Happy Happy Day postcard (or 2 or 3...) throughout the year. When everyone comes back to camp, I've seen these in the girls' bibles serving as placeholders/bookmarks.