Snail Tale Cards
It doesn't really matter what you write it on, or what kind of writing utensil you use. Just write it. And send it.
Then, eat some ice cream.
It doesn't matter how long...or how short...or if you spell words correctly. Just write a letter, and send it to someone you care about, or someone you just met, or to thank the convenience store employee that made a fresh batch of chicken fingers when your six year old dropped the previous order on the floor as soon as they were made.
Don't you just wish someone would write you a letter? Well, your chances of that happening increase significantly if you write one. Just sayin'.