Do It Before the Postal Rates Go Up
You have to gather a couple of items to celebrate Send an Empty Envelope to a Friend Day. You'll need an envelope and a stamp.
That might not seem like much, but when was the last time you used both of those things? Do you even own any stamps?
The envelope can be any size from standard friendly letter (Remember writing those in grade school?) to large manilla.
In a pinch, you could also use a postcard. In some respects, that might even be more fun.
Seal the envelope and stick the stamp on the front. Write your friend's address in the appropriate place and put it in a mailbox.
Your return address is optional.
I imagine you're already imagining many variations on this theme - each more devious than the previous.
Mwahahaha!
Nuf said.